I picked this up at a yard sale  last summer.  I paid $40  for it.  It seems complete.  Can someone tell me more about it and how to operate it?

https://imgur.com/a/4l2JkOc

Thanks in advance.

No image showing.

ETA Image now showing up. Don't know what the problem was, but suggest you load it into your OP rather than just posting a cold link.

Can't help you with that rifle, though.

I can't get images to load when I'm on my iPad.  The link is the only way I can get them here.

Looks like a target rifle. Image not coming back up, but I thought I saw front and rear peep sights. What do you want to know?

If it is in good overall condition and shoots... not a bad buy!!
It looks like a FWB 300s...
Here some info and history....
FWB 300S

have fun,
Ca_Longshot

That's what it is.  How do I load this thing?  What does it shoot?

It is a side lever spring air rifle with a recoiless sled system.  To cock and load, there is a button on the side lever that releases it.  The lever is pulled all the way sideways to the rear.  You will hear a ratcheting sound which is the anti-bear trap (it keeps your fingers from getting pinched).  The .177 pellet is loaded into the breach of the barrel with the skirt to the rear.  The lever is then closed.  The only safety is that the trigger will not allow it to fire unless the cocking lever is all the way latched.  There is nothing else to disengage.

Note:  This trigger is likely going to be lighter than anything else you have shot.  It is a two stage where the first is just the weight of the trigger blade.  It will let off very crisply, but due to the slide mechanism, the trigger will disappear from your finger.

Like with all spring airguns, you should not dry fire it, though the manual that came with them seemed to suggest that dry firing was relatively o.k.  But, I would avoid doing this. It is hard on the spring(s) and buffer.

ETA:  Although it will shoot just about any .177 pellet well, it is designed for about 8 grain wadcutter pellets.  These are the target pellets.  H&N Match Rifle, are the ones my rifle seems to like.  Though for something to get easily and at Walmart, the Crossman Premier 7.9 grain, or even the Hollow Points generally shoot quite well.

I’m ordering pellets tonight.  Look out chipmunks and squirrels!  Thanks for helping me out!

The FWB 300S is a 10 meter target rifle.  It pushes the 8 grain pellets at about 580 to 625 ft/s.  The velocity depends upon how much wear and use the spring, and buffer have, along with actual pellet fit.  It is not designed for shooting critters so much.  For this, I'd keep to chipmunk, and starling sized critters.  Domed pellets actually work a bit better on critters than other more exotic shapes.   The rifle will be capable of head shots which is what I'd recommend if shooting squirrels.

If you decide to mount a scope, make sure it has an adjustable parallax down to 10 yards or closer.  Also, shoot a lot of targets and learn the trajectory.  I'd be inclined to sight in at 20 to 25 yards or so.  This should be about at the top of the trajectory, and where hold over is least critical.

Just a little follow up...
Here is a link to FWB site..
It lists the FWB 300s original owners manual in pdf form!

FWB 300 s manual

hth,
Ca_Longshot