I'd strongly suggest checking out the appropriate volume of the Scott Catalog from your local library, and using it to make sense of and sort what you have. You can also use stampworld.com , that site does a very nice job of listing stamp issues in chronological order (though it doesn't use any catalog numbers). If non-USA stamps are something you want to pursue with any level of seriousness/consistency, be on the look out for catalogs from Michel, Yvert, Stanley Gibbons, AFA, Sakura, etc and/or country-specific specialist catalogs (for Poland, Fischer is the likely go-to);
ebay is a good source for these, just don't overpay. For USA, Scott is the best choice.
And as a word of warning, ignore the catalog values, they're grossly inflated for all but the rarest issues.