Polish genealogy is split basically in three because of the partitions done by the Russian, Prussians, and Austrians. I would recommend learning history and about all the border changes because it can get confusing real quick. (One day you’re in Prussia, the next Russia). With each section, I will give resources I’ve found helpful and how I find them helpful, I’ll explain the challenges I have for the region and lastly a basic outline of the history.
Prussia is undoubtedly the easiest to research in, they have the most resources out of any region. I always start with FamilySearch Wikipedia because they give a quick rundown of the history, culture, and most importantly resources to use. The top resources I use are as follows, Poznan Project, this is a database that has marriages indexed from the Historic Poznan Duchy. Prussia’s Polish population was a majority Catholic population and record loss is very minimal. The challenge I’ve had with Prussia is that most records aren’t digitized but indexed, so names can be taken liberally as the indexer might not know the surname.
I nicknamed Galicia the land of fire! Because there’s so much record lost during WW1 and WW2 devastated this region which was already historically poor. Most Polish-Americans trace their ancestry to this region just for the reasons stated above. Outside of FamilySearch, I like Gesher Galicia, it’s a decent database and welling organized, I would also recommend that you look at maps as names partially in this region change and many villages have very similar names, like Olszana and Olszanka. The only challenge I have for this region is record lost, I have 2 2nd great grandparents whom villages were razed by the Germans and Russians.
I’ll be honest I have no real experience with Polish-Russian genealogy, mostly because I can’t identify where my ancestors were from, so I would recommend that you get your family to take a DNA test and hopefully you can rebuild a tree far back enough to find a home village. If you do identify your home village I would check JewishGen and Redite ad Fontes both are amazing resources for Russian Research. If you ever hope in finding your family in the Russian partitions then I would look at learning cyclic Russian.