Aligning at the left the lyrics of a note one below other

Click the lyric, open Inspector, set the alignment

But do not, unless there is some very special reason to do this, it violates standard rules of music notation. Lyrics syllables are supposed to be centered unless notes unless they represent melismas - syllables stretched over several syllables. MuseScore already handles this correctly by default, and it's considered and import aid to reading to have the syllables align this way. So again, unless there is a special reason to override the default, it's better not to. But in the special cases where there is good reason, indeed, the alignment setting in the Inspector is the way to do it.