Nice watch. The reference will be in the inside case back (if you don’t know how to open, best to bring it to a watch maker).
I am no expert in these references, but looks like a nice original example, down to the crystal which has the omega logo in the center. A small polish of the crystal (not the case!) will make it look even better.
Once you have the specific number you can search for eBay sold listings, or on past sales on the forum for a idea of value.
These references are normally fairly common, although they have plenty of variations on dials, indices, markers etc.
The date version is also more common, so having a no-date adds a plus. Note that your version has a coat hanger S in the seamaster logo, so likely early DeVille I think (like 1962-63). It looks gold capped so this is reducing the value vs. full 18k gold or perhaps even a steel one. But it looks like in very good condition. Do you have box, papers or anything else?
Otherwise, a small introduction on you or how you got the watch never hurts. It actually helps getting answers. Welcome to the forum.