Especially where there is lots of activity in a MOO it can be a bit difficult because you have to read fast before the text scrolls off your screen. You connect to a MOO using a client program. This client can be as simple as a normal telnet program. That is when somebody says something to you in the MOO this text may appear in the middle of the line you are just typing. It is therefore preferable to have a specalized MOO client program.
MOOs are very informal places.
After a short while you will find out that you don't care much about spelling mistakes, upper case and lower case because the speed of communication is the main issue. As I said a room and everything in in is described as text. When you enter a room you see its description. This description contains also all objects in that room, other people in the room and objects you can interact with. It also describes exits to other rooms.