Graphing the trig function from to given points?

Hi all...I'm a bit confused about my new Math chapter. In this chapter we start to graph the trigonometry functions. I'm a bit stumped with that alone. Unfortunatly it's an online math class and I have no real outlet to ask any questions.

Anyway...

I have a problem that states.

"Find and graph the function of the form y = a sin x that passes through (3pi/2 , -4)"

I have no idea on how to even start.

Could someone give me some pointers on how this is worked out? Maybe even some calculator tips!

Thanks for your help.

Neil