This Revisions... button is a button for setting to use the Revision function of Quartus II.

The Revision function creates a compilation result for each Revision when using the same design file and applying different settings and constraints.
You can easily switch between Revisions and compare compilation results.

When Revisions are created, a .qsf file is created and managed for each Revision in the project folder.

For details, refer to the Quartus II Handbook at the URL link below and search for the keyword "Revison".
・ https://www.altera.com/en_US/pdfs/literature/hb/qts/qts_qii52012.pdf (English)
・ https://www.altera.co.jp/en_JP/pdfs/literature/hb/qts/qts_qii52012_e.pdf (Japanese) Old Version