Well I would advice you to get a semi acoustic guitar in the first place rather than adding a pick up later. Addition of permanent pick up can destroy your guitar’s sound and finish. SO BE CAREFUL
It's much the same as a 6 string guitar E A D G B E low to high except the 4 lowest pairs of strings are tuned an octave apart. Be careful, not all 12 string guitars (especially old ones) are designed to be tuned up to this pitch. Some have to be tuned a note or two lower.