What is an Olympus OM10 like?

It's a good little camera. The stock camera is an aperture priority automatic, which means you choose the aperture (lens opening) and the camera chooses the shutter speed. It's capable of full manual with an add-on shutter dial that plugs into the camera on the front left as you hold the camera and look down on it. If yours doesn't have that, it's no big deal.

The Olympus SLRs enjoyed decent popularity in the late 1970s, but were never as common as the Canons, Nikons and Pentaxes of the day. The advent of autofocus and now digital SLRs has driven down the price of all makes of film SLRs, so if the camera works well, you could probably find good lenses without spending a fortune. You shouldn't spend a fortune because this technology is old, no longer supported and not worth a big outlay.

That said, it's still capable of taking good pictures. Have fun!

The OM10 is a pretty good beginner camera. It is aperture priority, so the photographer sets the aperture and the camera decides the shutter speed. Unfortunately, Olympus did not have a huge following in the SLR market (they were also much later in the market with an autofocus SLR than its competitors), so the availability of lenses for it is small, and they will be fairly pricey.