Aye, “standard” Japanese is Kanto dialect. Tokyo dialect, to be specific.

There’s a reasonable difference between the two, but speakers of either will probably be able to understand the other. Biggest differences are the copula だ in standard Japanese becomes や in Kansai, and S sounds often become H sounds. So for example, そうだ becomes ほうや. Google-sensei can probably furnish you with a more extensive explanation. One of the fun differences is a variation in the pitch accent, so while in one dialect, “HA-shi” is “chopsticks” and “ha-SHI” is “bridge”, in the other dialect, it’s precisely the other way around. Never can remember which is which, sadly.

There’s also a few words unique to the Kansai dialect. Here’s a fairly extensive list: https://www.nihongoresources.com/language/dialects/kansaiben/wordlist.html

Pretty much every prefecture has its own dialect – most would be able to understand standard Japanese just fine, though. When you get into the furthest reaches of Okinawa or Hokkaido, though, the dialectical differences start to get pretty significant (both used to have their own languages until comparatively recently). I’ve been learning Osaka dialect myself. And Hiroshima dialect, in which だ becomes じゃ, and から becomes け, so だから becomes じゃけ, which sounds like something else altogether…