Maybe your personal trainer tells you to use a wider grip on the barbell. That’s an internal focus. If they instructed you to place your hands closer to the weight room’s walls, the focus would be external. The instructions are the same, but a study published in the Journal of Strength and Conditioning Research suggests the outcomes might be different.
On separate occasions, researchers directed 8 male and 4 female competitive athletes to perform the snatch for 3 reps using 80% of their one rep max. When the focus was internal, subjects increased elbow velocity. Internal focus also tended to make subjects squat too soon. Barbell velocity increased when external focus was used.