The following is a list of various documents and articles relating to proxies and their usage. Feel free to browser through and take what you want.
In the simplest form, a proxy is just a courier of information. You give it information, it takes it to someone, that person gives you information back, and the proxy brings it to you. There are multiple diferent types of proxies, from HTTP to IRC to Socks. However they all essentially do the same thing, and that is act as a middleman for your connections.
You may wonder why this is of any use. Well a proxy acts as a buffer between you and whatever server your computer is interacting with. This can be extremely useful for a number of reasons, first and foremost, it protects your privacy, secondly it can allow you to surf wherever you like unhindered by local restrictions. In some countries like china certain sites are blocked from public view, however proxies arent, so the proxy can provide a way to retreive the information you are stopped from accessing.
When talking about proxies there are two main categories, Transparent, Anonymous and Elite. A transparent proxy gives the server you are connecting to full information about who it is transfering data for. This means that you have almost no privacy. Anomymous means the proxy does not tell the server who it is transfering information for, however it does identify it is a proxy. This is sufficient in nearly all situations, as it provides the protection you need to keep your details safe. The last type Elite is the best, these proxies do not provide any hints that it is infact a proxy, as far as the server you are connecting to is concerned, your computer doesnt even exists and it is only talking to your proxy directly.
Every HTTP proxy can be organized into levels. These levels are standardized to be from 1 to 5. Where 1 is the best, and 5 is the worst. The higher the number the more information the proxy spills to say that it is a proxy. Level 1 and 2 are however almost identical in nature, so therefore are both Elite. A level 3 is borderline, and level 4/5 are obviously a proxy.
The other useful type is a socks proxy. These proxies give absolutely no indication they are a proxy, and give far more flexability over usage. These can be used for anything from IRC connections to hiding your presence on P2P Clients.
Socks 4 Protocol
One of the original documents describing the protocol
Socks 4A Protocol
The addition to the original document
Socks 5 Protocol
The original memo describing the workings of the protocol