If your goal is to be able to improvise solos, then you should learn scales first. Scales are the building blocks that solos are made of.
Tips for practicing scales
- Start by learning an easy scale, like A or E minor pentatonic shape. You can find them in-app from Learn → Workouts.
- Play the notes of the scale in different order; up/down, repeating some notes and jumping over others. Concentrate on melodies instead of speed.
- Play over some backing tracks, e.g. in YouTube search for A minor pentatonic backing track, and practice soloing over that. Again, forget speed, concentrate on playing in good time with the band (listen to the drummer!).
- Learn some licks from your favorite guitarists and try using them in your solos.
- Some other useful scales to learn include blues, major, minor, dorian and mixolydian.
Tips for fretting
In order to fret without pressing other strings, you need to adjust your fretting hand position so that your fingers are almost parallel to the fretboard. That usually means you have to move your thumb more to the center of the back of the neck and turn your wrist to a steeper angle.
That might feel uncomfortable at first, so remember to give your hand a rest if it starts hurting. The optimal place to press the string down is right before the fret, not on top of it.
Next up: Should I use fingers or a pick?