These are suffixes used after a persons name.

Sama

This is a word of the highest respect.  You use this with very important people.  Also a maid may use this term to the people she works for.

Sensei

This word is traditionally know as the word "teacher", and it is, however you also use this word for doctors, or anyone else who is skilled in their profession.

San

This word is the most common suffix. "Mrs/Mr" >_<

You use it with anyone older than you, strangers, and anyone you want to show respect to.

Senpai

This word is used for upperclassman. Anyone who is a grade or more higher than you, you can use "Senpai". 

Kun

This word can be used toward girls and boys.

First, the word is commonly used toward boys in your same class, or boys that are younger than you.

Second, Teachers and such may use this suffix after their students name regardless if it's a boy or girl. 

          Chan  -^_^-

This suffix is generally said by children or to children, but highschool girls also call their "girl" friends with this suffix too.   It could also be used toward boys but it's generally                used with a cute nick name.

 Also it can be used with a pet's name.