The Beginning, Play, Pause, Record, and enD buttons work pretty much as you'd expect them to. In playback, if a region is selected, playback will stop when it reaches the end of the selection. If the loop button is depressed, the playback selection will play over and over. You can type b, p, space, r, d, or l instead of pushing the buttons.
In the default configuration, Record and Pause are automatically depressed whenever you create a new file, and Play and Pause are automatically depressed whenever you read in a file from disk. If you don't want any buttons to be automatically selected, unset the One Touch Play/Record option on the Audio Tab of the Options dialog.