If you mean, how to create a score for piano with both treble and bass clef staves, simply select piano as your instrument, or use the grand staff template, when creating your score with File / New. If you've already started a score for another instrument, or using the sample blank practice score that you see when you first fire up MuseScore, you can add staves using Edit / Instruments.
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What are bass lines?
If you mean, how to create a score for piano with both treble and bass clef staves, simply select piano as your instrument, or use the grand staff template, when creating your score with File / New. If you've already started a score for another instrument, or using the sample blank practice score that you see when you first fire up MuseScore, you can add staves using Edit / Instruments.