Let’s say you have these N sucessive commits: 1, 2, 3 and 4.
If you select the commit 2 and choose “Revert to this revision”, your working copy will contain the changes brought by commits 1 and 2. Commits 3 and 4 will be “canceled”.
If you select the commit 2 and choose “Revert changes from this revision”, your working copy will contain the changes brought by commits 1, 3 and 4. Commit 2 will be “canceled”, or rather, played in reverse on the top of commit 4: if a line was added, it will be removed. If a line was removed, it will be readded.