Before scheduling an appointment at a mechanic, how would I go about finding, and possibly fixing, what I've determined to be a coolant leak?

Had some engine overheating issues recently that I thought might have been due to my oil change and cabin air filter replacement past due. Got filters replaced, got my oil changed, drove around for a bit, then the car started overheating.

Noticed the coolant reservoir was drained. Thought was odd since mechanics usually check fluid levels with an oil change. Bought some coolant, filled it up, everything was great.

A couple weeks later, engine overheating. Checked the coolant reservoir, and it needed to be filled again.

So I'm sure it's a leak. Is this something I'm able to correct on my own, or do I need to bring it in?