Ehm... You press E, then press F to defocus, use wasd to turn camera around, scroll to zoom, all displays with stats will be on the left and right. Select "tools" with 1-0. Click and hold on parts you want to interact with, then use numbers to select how exactly you want to interact. Use X to select mode from fully mouse driven to fully automatic (speed adjusted by dragging hexagon cursor thingy up and down). You can apply cock rings to subjects by pressing Tab when interacting and dragging the item on the paper doll. To use dildos, first equip them in your inventory bottom slots, they will appear in 1-0 menu when interacting.
There is a comprehensive tutorial, you can activate it in Options by selecting Show tutorial drone (you can find it near delivery gate and requisition person).