- As Panko said, just linking to a couple of places where it talks about what Pump.io is and how to find people shouldn't hurt. It's very related to this software and its proper use.
- The posts in the Messages tab are not necessarily private. They're messages addressed to you, but they can still be sent to more people, or be public.
- Where you say "You can also follow people that you follow along by clicking on the followers tab", I guess you mean "also follow people who follow you, by clicking on....".
- I think the sentence "On To Button whom will you send the message" could be reworded to be clearer. Something like "Click the 'To' button to select who will see your message". Also, there's no problem with this field being empty. What is recommended is that the post be sent to Public, to avoid the problems with comments in "followers only" posts.