Kekkei Genkai (Bloodline Limit) - abilities only possessed by specific people A.K.A. Ninja Clans. This power is genetically passed down from generation to generation, which means you can possess all the Nature Elements you want, buy you can't use the Kekkei Genkai if you don't have it in your blood.
Kekkei Tōta (Bloodline Selection) - this one is very different from the Kekkei Genkai, because it's not a "Limit", it's a "Selection", which means it's not limited to specific people as I mentioned before, but a simple selection of Nature Elements combined together. Simply said, anyone can learn it if they possess the specific Nature Elements. Hiruzen knows to use all the Nature Elements, but he doesn't know how to combine them in one - Ōnoki, if you din't know, didn't just learned how to use the three specific Nature Elements for the Dust Release (Earth Release, Wind Release, Fire Release), but he was thought how to combine them in one by Mū.