Welcome to the forum waltribeiro.
The short answer is that generally you don’t worry about rests - put the notes where you want them and Dorico will figure out how to handle the rests automatically.
You can click notes in where you want them, using the rhythmic grid above the stave for precision, or you can use the caret (select the first rest and hit Enter or Shift-N, then use arrow keys to move it to where you want the notes, or just double-click on the stave where you want to put the caret).
This is all comprehensively explained in the manual: Inputting notes
Note that the 3.5.10 manual I’ve linked to is much more recent and much more substantial than the Dorico v1.2 manual you’ve linked to. I recommend bookmarking the 3.5.10 manual, as Google doesn’t reliably prioritise the most recent manual in its search results.
If you really need to force rests you can hit comma (,) to turn on rest input, then type O to turn on Force Duration, then the note value of the rest you want (which is the number keys 1-9, shortest to longest), then Y or any key from A to G (or on a midi keyboard) to input rests. Once you’ve turned on Force Duration and Rest Input they’ll remain switched on until you toggle them off (again, with “,” and O).
But let me repeat: 99% of the time you don’t need to input rests at all. It’s different to the way other notation software works and might take some getting used to, but in the long run it’s a real timesaver.