Future simple and idiomatic

"Will" & "Going to" are used to express the future 

"Will" is the sense of planning and likelihood of an action happening

Example: 

Andrea will play guitar tomorrow 

Negative:

Andrea will not play guitar tomorrow

Question:

Will Andrea play the guitar tomorrow?

"Going to"

Is used for specific plans when you are sure that 

Example:

Richar is going to take an music class

negative:

Richard isn't going to take an music class 

Question:

Is Richard going to the class of music