I don't understand the MP5 settings.

Hint 1 of 3:

The first setting (the one closest to you) is the off setting.  This is also
known as "safety-on".

Hint 2 of 3:

The second setting (the one in the middle) lets you fire one shot per one
pull of the trigger.  This is also known as "semi-automatic".

Hint 3 of 3:

The third setting (the one farthest from you) lets you fire as many shots as
you want with one pull of the trigger.  This is also known as "automatic".