#1
I'm looking to get an atmospheric-like tone but I don't know so much about pedals and what the effects actually do. What effect should I go about using if I were seeking an experimental, ambient, psychedelic sound?

Currently, I just use distortion but that's not quite what I'm looking for.
I really like the sounds Radiohead and Mogwai produce.
#2
fuzz, a good digital reverb, phaser, a deep chorus, delay...

id start with a fuzz, its going to be like that distortion you like, but its going to be that more over the top sound i think you are looking for. i personally think a nice digital reverb is good for experimental stuff. you can get some wierd ambient sounds if you set the mix to mostly/completly wet. i liked the verbzilla for that stuff when i tried it.

for chorus, you can either get something like a nice shimmer, or that deep throbbing sound. phaser is a kinda whoosing sound, try a phase 90 and a small stone. delay can add just a touch of depth (short) or a whole new dimension (medium-long).

id just say go try a bunch of pedals in a store to see what you like. but those are some good ones to start with.
#3
Thanks for the advice.

I'll definitely look into the phase pedal and some delays.