I'm not sure why you're having a problem. I'll assume that you are not putting the images in text boxes.

Word's default is to format inserted pictures as "in line with text." If you insert one image, then a second, with no keystrokes in between, the images will both sit on the same line as long as their combined width fits within the page margins. If not, the second will jump to a second line. Sizing down one or both images will resolve the problem.