That’s why the SSi method breaks it down into simple steps, without worrying about grammatical terms.
As for “Rydw i…”, I think it’s fair to say that that is never used in conversation. You might meet it in books. People will understand “dw i …” or variations like “rw i” or just “wi” (esp. in the south).
The verb “to be” (“bod”) is pretty tricky in Welsh, and traditional grammar books don’t really help all that much.
Those by Gareth King are somewhat non-traditional, and help a lot more, but are probably best left until one has got well into the SSi method first. (I believe there are some other good books around also, but I haven’t tried them).