You cock it by pulling back on the "hammer", which is really the release that allows the "slide" to pivot forward. Pivoting the "slide" forward compresses the mainspring. In position 1 shown below, the "slide" is cocked to the low power setting. Continuing to open it forward to position 2 compresses the spring to full power. The barrel is mounted in the slide and pivots up with it. The breach where the pellet is inserted is about 1" forward of the aft end of the "slide", so there is plenty of room to get a finger in there to load a pellet and push it home. Lowering the "slide" and latching it down with the "hammer" makes the gun ready to fire.
