Hi just bought a non-branded android phone that looks like a samsung but it's just an android.  I have mucked up my desktop screen, how to get back to original?

the four symbols that stay constant at the bottom of the screen (phone, contacts, messaging and applications), I have somehow managed to get rid of messaging!  And don't know how to get it back.  I now don't know how to access my text messages as there is no button now for it!

How do I restore to factory settings, is this the only option?

Also when I press my applications button, not applications appear, they used to be there, nothing appears when I swipe etc HELP!

Maybe I shouldn't have entered into the land of android and stuck with my boring non-smartphone, I not so smart!