How do I save text in .txt file in internal storage?

hello guys, i'm making a note app for tablet that is in portuguese for now, but my biggest question is how can i save in .txt on internal storage

What do you mean by "sdcard"?
If you mean a removable (mircro) SDcard you can't, because since Android 4.4 (KitKat, API 19) this is read-only.

See also here:

sorry for my mistake, it was for the internal storage, i just literally forgot the internal name and people usually say sdcard

Show your blocks (as mentioned in my guide "How to ask a question ...").