You really need to show some starting code
and a screen shot of your game idea.
Eg what is your game? side scroll / top down / isometric
What is your control idea?
What is your character mechanic. Separate Gun / Body / Head
Basically though the angle of your character , or where your character is looking, will be (or can be) defined
and you just need to use that angle to set the bullet angle of motion when firing