go to front view, press shift+a->Images->background. Then select your image. Goto side view(I prefere right side or numpad3) and do the same thing. You can use reference instead of background. The difference is that Reference by default will show no mater the angle. Background will only show when you are in that view. Also background by default shows in back. I personally change this to front then check opacity and set it between 20 and 60 depending on the image. These settings can be found in the data/Empty tab of the properties editor. Then you just have to move them into position just like any other object. Some people like to move the images physically behind the mesh building area. Like a meter or 3. The front would be on the Y axis and the side would be on the x axis. It’s a matter of taste.
