How do I connect to mobile network?

Excuse me, I'm having some trouble connecting to the mobile network on my device. Could you possibly walk me through the steps I need to take to establish a stable connection? I've tried turning the phone on and off again, but it seems to be stuck on the searching for network screen. Is there a specific setting I need to adjust, or perhaps a problem with my service provider? I'd really appreciate your help in resolving this issue.