"Can anyone tell me the eviction process?"
No one can or will walk you through this process over a message board. You need to do research of the statutes or talk with a local real estate attorney (assuming you can't sweet-talk a clerk in the landlord-tenant court to walk you through it).
"I was told to start by sending a certified return receipt letter demanding a pay or quit letter but it doesn't specify how long I have to give them? 3 days or more?"
First, you don't have to send any such notice via certified mail anywhere I know of. As for how many days the notice must cover, that's state-specific.
".... since I can't afford an attorney."
If you didn't want to familiarize yourself with the various aspects of becoming a landlord and did not set aside money for possible problems, I'm afraid that you should not have gotten into the investment property game. You need to hit a local library and start looking at the statutes, and also hit the local courthouse. Since these things are a matter of public record, you can look over someone else's eviction case paperwork.