I.D'ing a frame

Please excuse me if I’ve posted this before. I did do a search.
What is the best way to I.D a frame?
What do I need?
Where do I go?

You get the picture.
Thanks

Try looking for serial numbers on the bottom bracket first.

The “retro” dudes at on the www.bicycles.net.au forum are usually a good source of knowledge or migth be able to point you in the right drection.