"How do I start organizing"
Literally just get two or three friends and start showing up to stuff
Big march? Your team make sure you all get home
Protest camp? Combination movie night and care package party
Heat Wave/Cold Snap? Go give out hot and cold drinks. Pretend it's a party to dodge rules
The boring truth is that to get anything good done in even the smallest significant way you have to show up and keep showing up again and again and again and for longer than you might think.
You don't need tons of theory, you don't need guns, you don't need fancy tools
Do the little things you can achieve now. The stuff down the line will get worked out as you get good at the little stuff