It's a horrible hobby...don't start into it...LOL!
First off...if you're 18yrs+, get age verified. If not wait...sorry.
If you are...continue on:
Check out TTAC3 (Davenport/Ossignton) and Defcon (VP/Steeles). Not sure if Sgt. Splatters games will startup soon. Defcon has a new field at Downsview park I think.
Can't recommend TTAC3 more highly.
CQB (bloor/landsdown) is a great place. Some guys have come out for their first time there...but they're usually brought along by a guy who's been around a bit. If you're level headed and fight hard...there's no barriers.
Most other outdoor fields are out of the GTA.
Some teams are "clubs" that train/meet together regularly...but others (probably most) are loose collections of guys who just play at games together.
Most of the figuring out of AEGs is done through trial and error (expensive), researching (Google, here, other sites, Mechbox.com), or just chatting with others. Some guys fiddle with them A LOT...other guys just add bbs and batteries and want to play.
I've run AEG workshops in the past...where I run through how they work, how to tune them up, what does what, and a bunch of other stuff. I'm not sure if I'll run another one this fall...it's a horrible amount of work.
Best of luck,