how can I calculate inverse sin, cos, & tan on here?

First you need to know that inverse cos is the same as arc cos

that is  $$cos^{-1}\theta = acos\theta$$

Now, there is 2 ways to bring up acos,

You can press '2nd' then 'cos' which is the same as most hand calculators work

or

you can press 'cos' just a little longer than usual and it will display as acos

The display is in the display bar at the top.  Give it a go and you will see what I mean.