Thrust force is a combination of the swimmer's kick as well as the swimmer's arm pull. Both element's help to displace the water to propel the swimmer forward.
For the arms, the placement of the hand on the water's surface will dictate the direction of the thrust force. The picture shows drag force and lift force; thrust force is the resultant force of these 2 elements. Ideally, thrust force will be in the desired direction (forward).
For the flutter kicking present in freestyle, the resultant force is what propels the swimmer forward in the water. The thrust force primarily comes from the swimmer's hand and arms, with a smaller amount coming from their legs.
picture 1: https://www.real-world-physics-problems.com/physics-of-swimming.html
picture 2: https://www.researchgate.net/figure/Representation-of-the-action-of-the-thrust-and-vertical-force-during-the-flutter-kick_fig2_233972563
information: https://www.real-world-physics-problems.com/physics-of-swimming.html
picture 2: https://www.researchgate.net/figure/Representation-of-the-action-of-the-thrust-and-vertical-force-during-the-flutter-kick_fig2_233972563
information: https://www.real-world-physics-problems.com/physics-of-swimming.html