master data in ax 2012 - and transaction data

HELLO,

1st: I Want to know what is master data  in AX 2012 R3, for what we use, if  its a function or form in Dynamics AX as a module or what,

or if its a system linked to the AX?  

2nd: what is transaction data in AX 2012 R3? FOR what we use if 
and also if it is a function or module we use it in AX 

how its work 

and show the steps 
and the purpose 

and how those two help us?

thanks>>>...