CustomBooks

Confusion on Save, Post, and Save and Post

Hello, 

I am not sure what the difference between Save, Post, and Save and Post are. 

I was entering items, price matrix, and adjusting inventory. 
What are the differences between Save and close, Post,  and Save icon?
- Does 'Save and close' means not posted and I still have to post at some point?
- If I 'post', does it mean 'saved' too?

Please explain.