Yup, you've got it.
There are two sets of compass directions:
1) Course: This is an absolute direction. It is the number of degrees you are heading from true north. A course of 0 degrees is due North; a course of 180 degrees is due south; a course of 90 degrees is due east; a course of 270 degrees is due west.
2) The bearing to the target. This is a relative direction, independent of your course and based completely on the target's direction relative to your bow. Your bow is simply considered to be pointing to zero, regardless of whether you are actually heading north, east, west, or south. A bearing of zero means the target is directly in front of you; a bearing of 90 degrees means the target is directly to your right; a bearing of 180 means they are directly behind you; a bearing of 270 means they are directly to your left.
As you have noted, the bearing of the target has absolutely nothing to do with the course of the target. If the target has a bearing of 180, he's directly behind you. But he could be gaining on you, running from, or crossing your path.
By the way, you shouldn't feel bad about this. If you watch the film "Das Boot" very carefully, there's a scene where they are being depth charged and the captain, an experienced and wily skipper, is doing the maths under his breath: "238 degrees minus 45 . . . "
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