Your first picture shows the complete large primer slide, as well as the wheel, and pin from the small primer slide (the broken part in your 3rd picture). The other part is the spring that connects the primer slide to the base.
Your second picture shows where the primer slide should be installed. The wheel fits on the cam rod (the bent piece that threads into your press base). This is what actuates the primer slide in conjunction with your spring from picture #1.
This is all very clearly illustrated in the master parts and assembly instructions with your press.