But in general you can imagine that you can print in a resolution of around 0.1 x 0.6 x 0.6 mm.
You can also get better resolution by using a printing service, who usually have better industrial quality printers.
For one off prints this may also be a good option for you.

Sounds to me like the final size and what surface texture you want are important here. Have you got a picture?

How big should the model be?
Typical 3D printers have a layer height of about 0.1-0.4 mm, so you will see this in the result. If you want anything smoother you need to do after processing like sanding.
Resin printers are typically 100mm max.

There are two types of 3D printer currently in general hobby use. The FDM(Fused deposition) ones which heat plastic and build up the layers that way and the ones which use UV light to harden a layer in a bath of resin. Resin printers give better detail but for smaller prints and nasty chemicals ;)

I'm assuming you are not thinking of a resin printer.
200x200x200 mm is a usual starting size, but 300 is also possible.
You will usually start with .stl files which can be converted by a slicer program into the specific commands for the printer you have.

There is a huge amount of stuff for hobby groups, 3D printing, electronics & computing (including vintage stuff and restauration) and astronomy to name a few.