You may well find more comprehensive answers to your question in our Barge Buyers Handbook, available in the shop.
There are basically two types of mooring: Long Term and Short Term.
As you might expect, this is somewhere where you may moor your barge for more than, say, a couple of weeks. It could be a relatively permanent home mooring, to which you always return eventually after cruising, or a mooring at a location you are visiting for an extended period.
You should expect to need permission to moor long term, usually from the owner or manager of the bank, pontoons, or buoy you tie up to. The owner may be an individual, a business, a public or commercial moorings operator, or the navigation authority. You will usually have to pay for a long term mooring, although if the location is somewhere not much in demand (such as in a very rural area) and you make a good impression on the person concerned payment may be something informal like a bottle of Scotch every now and then. More often there will be a formal rent (e.g. by the week, month, or year), typically varying with the length of the barge but sometimes also with its width. You may also have to pay for the services you use at the mooring (such as mains electricity), and the rent may be higher at locations where more or better services are available (or which are more attractive generally).
You will generally have to sign a mooring agreement. In fact, it is in your interest to do so, as this will help confirm what rights you have concerning the mooring. Read the agreement thoroughly, and make sure it is acceptable to you before signing. You may find some unexpected provisions, such as that you are forbidden to do repairs or maintenance, or that you have to pay the moorings landlord a commission if you sell your barge while it is moored there. Don't be afraid to negotiate.
There are several services which you may need. The absence of some may simply be an inconvenience (for example, you may be able to cruise to a nearby water point), but the lack of others (e.g. security) may make the mooring unacceptable. Possible services (or attributes) are:
Protection. Is the location sheltered from heavy weather, currents, floods, etc.? If the mooring is tidal, are you happy to have your barge sit on sea- or river-bed for large parts of the day? Is the bed soft mud or pointy stone?
Security. Will your barge be safe from break-in or vandalism is it is left unattended for long periods?
Monitoring. Will someone contact you if he thinks your barge is sinking?
Access. Can road vehicles get near to your barge (important for deliveries or getting purchases on board without a long walk)? Do you have to use a dinghy to get on board?
Parking for your car (security is also an issue here)
An address for your mail
Telephone, a small problem in the days of mobile phones
Drinking water, with a hose connection so you can fill your tanks
Sewage disposal (with a pump, if you have an on-board tank and don't have your own pump)
Storage on land for possessions you don't have room for on board
Privacy (even a garden)
You will not be allowed to live on board at many long-term moorings. When a long stay becomes residential is a rather grey area, but it may become a consideration for you. Official residential moorings tend to cost more, but can give you more security (depending on the mooring agreement). On the other hand, not raising the issue may allow you to get away with it for a while where it isn't officially allowed. At an official residential mooring, you may find you are treated as a resident of the community and are liable to various forms of local taxation.
Although commercial operators may advertise moorings, there really is not an organised market. Typically demand exceeds supply. You can usually get a mooring somewhere fairly quickly but you may find it rather pricey if you have to rush. The best way to find a suitable, reasonably priced, and pleasant one is often to take your time and ask around (people on moored boats, the local navigation office or staff, etc.) in the area. DBA members who have visited the area in the past can also be a useful source of information.
Many barge-owners moor their barges for the 'winter', normally 1st Nov to 1st April, at a reduced rate and cruise through the other months
A short term mooring is one you use for a few days, generally for a stop-over while you are cruising. These are often free, but sometimes there is an overnight (or even hourly) charge. If services (such as electricity) are provided, they may be metered.
These moorings are usually first-come-first-served, and in attractive areas all of them may be taken by lunch time! However, if there is a shortage, and sufficient channel width, it is reasonable to ask the skipper of a moored boat whether you may moor alongside. There may be a maximum length of stay (sometimes with a penalty charge for overstaying). Overstaying tends to make you unpopular surprisingly quickly in a busy location.
The normal rule is that, unless it is indicated otherwise or it would be impede navigation, you may moor short term to a towpath anywhere. But, if in doubt, ask. Beware, though, as it may be too shallow to get alongside. You normally may not moor to private property without permission, or at lock landings.
There may be a maximum length of time you may moor.
On the other hand, moorings which are short term in the busy season may be available long term (often for quite a reasonable charge) for the off season by arrangement with the navigation authority or mooring manager.
Barges >20m are not technically 'pleasure craft' in the international regulations (CEVNI) so may be able to use a commercial mooring if it does not interfere with the commercial barges.
It is possible quite legitimately to do without a long term mooring completely, and even to avoid paying for short term moorings, by keeping on the move and using only free-of-charge visitor ones as you travel. But the navigation authorities (and others) may get fed up with you if you abuse this process through such tricks as oscillating every few days between two nearby free mooring locations, as this tends to be seen as dodging legitimate charges.
There is an etiquette at moorings. The general rule is not to annoy other people. Here are a few tips:
Don't run your generator in the evening if it will disturb others.
Don't place your mooring lines where they can trip passers-by.
Don't strew rubbish about
Keep your dog under control, and pick up its droppings for proper disposal
If you moor alongside another vessel, use plenty of fenders. If possible, attach moorings lines to the bank as well as to that vessel, for safety and to make it easier for the other vessel to depart before you.
If you need only part of the vacant length of a mooring, tie up at the end of the length. If you tie up somewhere in the middle, you could divide the space into pieces too short for another vessel which could moor if the pieces were amalgamated.
Don't moor in such a way that it makes it awkward for others to manoeuvre or get by you.