Get a database like SCID (it is free). Capture the position in FEN (easy to transcribe position to FEN by hand, or if you have the diagram on the computer, use a capture program like the one on https://sites.google.com/site/fredm/). You can paste the position into SCID (edit/paste start board) and thus save the position for future review.
Advice on Tactics Database
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Hello,
I have been going through various tactics books and need to keep track of tactics incorrectly done on my computer as carrying around all the books is not always feasible. I need you help:
a) Should I create a PGN file.
b) Should I use some specific software.
Or is it some other way which is better which you might know.