Release the clip on the left side and let the slide pop back. Grab the front end of the barrel and push it down. load the pellet directly into the barrel. close the barrel. cock the gun normally and fire.
It is a single shot pellet gun.
There's a double action to the slide - see the link below for a manual:
.177 cal. Crosman, daisy, rws, beeman, marksman all make pellets in the .177 size
You can load as many BB into the repeater as it will hold, BUT only one pellet at a time can be loaded into the barrel. One shot one pellet.
Contact the maker for a replacement manual