1 the game has a kind of haze or mist,you can reduce it slighty by pressing f2 when you are playing
2 there are several clans, id say play.make friends first before you join any,
3 there are 2 types of tournament, one for all and one for subscribers only. you just enter when the tourney is running,press the green button for details,
4 the "ally" button is only useable if you subscribe, it changes the colour of your allies tank,making it easier for you to spot them.
5 it means maybe trying to use a programm that might increase your chance of winning, "cheat" in other words, dont do it
6 you can only post your avatar once you have subscribed your nick name,
7 subscribing will enable you to make your own ops"games" and also allow you to download the pc version of the game,
lag is normaly decreased because you dont get adds

sniping usually deals with nukes...and, if u know the map like u know ur finger (i don't like using the back of ur hand -.-), then u can shoot into that haze and hit the target... i do it all the time :-)  ask any i fight.

What does:
7/6 
Mean when you are playing.
Which is win and which is lose?

depends on what you are counting, the figure to the left is kills the one to the right is deaths,
when you play 1-1 it is generaly deaths that are counted, not kills,because some players would kill them selves just to make sure the oponent doesnt get the kill.
hope that was clear

:D once you have subscribed, to post avatar click settings on log-in screen...;)

Must you "Subscribe" by paying money, or just create a nickname.  I can not really find a page for creating an avatar.

Also, are there servers or websites for all of the clans?

Most clans have their own websites. Theres a post here somewhere with a few of the links. 
FTW's clan site is 

http://www.ftw-rocks.com