Focus is the direction your are giving your mind. As in keeping your mind on the intended project not allowing it to wander off while you do your visualisation. Visualisation can quickly become daydreaming without focus.
Visualisation, is the creation of a mental movie similar in texture and feeling as memories. You use your imagination to create a 'future memory" of the goal you have, having manifested. You use all of your internal senses, so you hear, feel, taste , touch and see what you would experience when you have reached your goal.
To successfully create a future memory of your goal you need to maintain your focus on what you are doing during the visualisation. If you lose your focus you can wind up daydreaming about things you don't want to experience and recalling the past experiences that didn't make you happy.
Once you've done your visualisation for the goal it's becomes a mere matter of remembering what you created.
Alex