Forth means "from now on." If you declare that from today forth, you'll pursue your dream of becoming a rodeo clown, it means you'll work every day to make it happen.
The adverb forth describes pushing forward, either literally or in time. When something goes forth, it moves into view or forward. In spring, flowers shoot forth from the ground. You have probably heard the expression and so forth, which like and so on means whatever else. Don't confuse forth with fourth, which sounds the same but means "number four in a series."