On the FamilySearch wiki linked to in the parent, there are also many country-specific guides that link to resources both inside and outside of FamilySearch. Those that may be of interest to you given the countries you mentioned:

- Germany: https://www.familysearch.org/en/wiki/Germany_Genealogy

- Ukraine: https://www.familysearch.org/en/wiki/Ukraine_Genealogy

- Russia: https://www.familysearch.org/en/wiki/Russia_Genealogy

Also see the main wiki page, which has a Locality finder and may have other links depending on how far back you want to go (e.g., German Empire): https://www.familysearch.org/en/wiki/Main_Page

And of course, search the entire FamilySearch database too, which aggregates many, many sources: https://www.familysearch.org/search/