Can I sue in small claims for a guy saying he would fix my truck and he took my first half of the payment but never returned?

Contrary to what people are saying, you do not need a written agreement--your testimony that there was an agreement is sufficient proof, especially since he appears to acknowledge the debt. However, you probably will want to make a written demand before going to court.

Here are the basics for small claims actions in California:

http://www.courts.ca.gov/selfhelp-smallclaims.htm

You will still need written evidence of an agreement, him on video exchanging money in front of your house is not proof of an agreement to how much he owes

You can, but unless you've got proof of payment and/or written evidence of your agreement, I wouldn't hold my breath on getting very far.