Sometimes it seems like the esperanto letter "c" is a simple "s" sound but sometimes, (like in pico) it sounds like "ts". Anybody know the actual pronunciation?
Yes. It's always how it looks. Since Esperanto is a planned language it's pronunciation will never ever change. Every single letter is the same in every sing word.
ETA: you might find this helpful/interesting too: http://en.m.wikipedia.org/wiki/Esperanto_phonology#Orthography_and_pronunciation
Would I be able to say it as th, or until I am able to distinguish s and c? Half the time it sounds like th to me.