I Gave up !!! How can I create these tripiets

4 (set duration of note to eight)
[Ctrl]-3 (make that eight note into 3)

OR

Enter an eight note or rest
Select it
(from the menu) Notes >Tuplets >Triplet

Where's the problem: that triplet is 3 16th in the space of 2, which is an 8th, so start with an 8th rest, then Ctrl+3. Enter the triplet notes, then the rest of the measure.
For the triplet you need to change the tuplet style to 'bracket' and 'above', and for the 1st 8th after a beam property of 'middle beam'