I personally think that permissionex is very complicating. I prefer groupmanager since its way easier promote people and make ranks, but that's just on opinion.

But this post isn't about how I think groupmanager is better its to teach you some commands.

Creating a group and giving it a prefix!

/pex group [group] add

/pex group [group] prefix [prefix]

That is how you make a rank!
Once you've done that you need to do...

/pex user [user] add group [group] set

That command sets that player/user the rank you give him/her

Ty for reading!