The use of a guild depends very much on the guild and its members. It can be a social group for people to chat with and play with. If you find yourself in a good guild you can make some good friends. Also it's fun to play with others, and haviong a good active guild means you have a group of usually similar minded people who's playing style you can get to know, as opposed to PUGs (Pick up groups) which can be a bit more hit and miss
If you decide you want to get into the PVP side of the game then really getting into guild that's active in PVP is a must. Yes there are some PVP areas that you can just join on your own, but the majority is group orientated, which needs planning and organisation
As for feeling noobish, we all had to start somewhere. There's a lot going on, and Factions throws it at you pretty thick and fast, so it's easy to find yourself lost at times
As sk8510 said, there's
http://guildwars.wikia.com/wiki/Main_Page which has pretty much everything about the game
There's also
http://wiki.guildwars.com/wiki/Main_Page which has almost as much, and which can also be accessed by pressing F10 in game and chosing a subject (minimises the game and opens a browser window)