The default is for a trill to be an interval of a diatonic second. In other words from the written note to the next note in the major scale indicated by the current key signature. If you have a 1 sharp key signature for example a trill on a D would go to an E (two semitones), a trill on a B would go to a C (one semitone), a trill on an F# would go to a G (one semitone) etc.

You can alter the interval in two ways - the right hand box in your picture allows you to select an interval other than a second. The left hand box allows you to alter that interval to something other than diatonic. So if you choose a third in the right hand box if you leave the left hand box as diatonic you will get a trill the next but one note in the major scale. Again assuming a 1 sharp signature a trill of a diatonic third on G will go to a B (a major third, 4 semitones) a trill on an A would go to a C (a minor third - 3 semitones). If you change the right hand box to be minor, trill on a G would go to a Bb (a minor third - 3 semitones. The trill on A would stay the same as it is already minor. If you change the right hand box to diminished, a trill on G would go to Bbb (a diminished third, two semitones) and a till on A would go to a Cb (a diminished third, two semitones). If you change the right hand box to augmented you would have a trill of an augmented 3rd (5 semitones) G to B#, or A to C##.

So to answer your question (finally!), it depends what you mean by 1/2 trill, what key you are in and which note you want to add the trill to.

See https://musescore.org/en/handbook/4/ornaments#properties for more information.