Yokomen-uchi is a diagonal strike to the temple or neck of tori.
When the strike is completed, i.e. immediately at the beginning of the technique, both partners are facing each other in Gyaku-hanmi position. In other words: Uke moves to the outer side of Tori's front leg. Unlike Shomen-uchi, Uke leaves the direct line for the strike.
Please note: Yokomen-uchi is not a hook; it is carried out in a straight movement.
This video shows the Yokomen-uchi attack with a pivoting entry by Tori (ends in the position Ai-hanmi):