Our SO reserve program does not require POST certification. Reserves are sworn in and legally have same powers as full time deputy, but by department policy requires to always be under the supervision of certified full-time deputy and does not allow a reserve to make an arrest while not working under that full time deputy. What "supervision" means can vary big time big time.
Your duties will depend on trust earned with the full-time staff. Some reserves drive vehicles and 10-55 with full-time deputies on calls, some are on SWAT or other special groups. There are also other reserves that are not capable for a variety of reasons that simply look good in public at car shows and stuff. Most of the reserves do a combination of filling in at public gatherings and riding with a full-time deputy dual. It's up to that deputy what they want the reserve to do when it comes to handling calls, suspects, evidence, whatever.
I have had a bunch of guys that get really interested in joining when they see that reserves actually get opportunities to do some really cool things. Also, most applicants just want to serve the community.
We get a steady flow of applicants and because of the wide range of possible duties, that's pretty helpful to pick guys for what is needed. The reserve classes are usually filled with a wide variety of people from former military, to old and retired. There's a job for everyone.
That's probably more info than you wanted. PM me if you want the SOP. I shouldn't have an issue getting a copy to send to you (at least the reserve portion).