How do I check a users level using a function or php?

I have tried a bunch of different code from the support here, but I just cannot figure out how to check a user's access level using PHP or a function.

Went through this post and tried everything:

my code:

if(current_user_on_level(4)) {
echo 'show something';

nothing is showing to either a user who is on level 4 or me, the admin. Both logged in of course.

Any help please?