Bookmarks are somewhat like registers in that they record positions you can jump to. Unlike registers, they have long names, and they persist automatically from one Emacs session to the next. The prototypical use of bookmarks is to record “where you were reading” in various files.
Comamand about Bookmarks
C-x r m <RET> Set the bookmark for the visited file, at point. C-x r m bookmark <RET> Set the bookmark named bookmark at point (bookmark-set). C-x r b bookmark <RET> Jump to the bookmark named bookmark (bookmark-jump). C-x r l List all bookmarks (list-bookmarks). M-x bookmark-save Save all the current bookmark values in the default bookmark file.