Typical 35mm lens unknown focal length or mm

note the numbers near the back or bottom of this lens
they are F Stop settings or lens apature openings
this particular lens opens wide at 2.5 and shuts down to F22
so it is a good quality lens allowing low light photography with the wide open point being 2.5
remember the 2.5 is the large opening
the 22 is the small opening

for depth of field use the smaller opening F22
keeps all in focus from Camera to Infinity

Note the front ring has feet and milimeters, on the milimeters scale you see a figure 8 which is sideways, that symbol is infinity.
Infinity is beyond the eye.

Another tip
When you focus to infinity in other words as far out a focus as you can get, barely bump the lens back from infinity, you can actually over focus at infinity, just a hare though