Navigate to the handbook page for MuseScore 3: Text
The previous chapter covers text that affects playback tempo, but there are many other types of text available in MuseScore: lyrics, chord symbols, dynamic markings, fingering, figured bass, headings, rehearsal marks, plus many more. These are all accessible from the main menu via Add → Text.
For short generic text, use staff or system text. The difference between these two texts is whether you want it to apply to a single staff, or the whole system. This makes a difference when extracting parts.