OTE is a good site,its very big and you'll probably play 6-7 different games,maybe more,it was a while ago i played there.
Rec-reationall-ball,is playing for fun at weekends with your mates,before you become addicted, and you will. then you decide want to see how good you really are and form a team,then you play tournyball,i think thats what you mean by feildball.
couple of first time tips- wear gloves,not big biking ones cause youll never get your finger on the trigger,wear boots or something with good grips.
as Genetic says,if your gona start playing reguarly get some good gogs as it will change your whole game.
most of all have fun and if your nice to marshalls they'll be nice to you