Moving one MC inside another MC

I’m working on my very first game (outside of tutorials) and it’s going to be a tower defense style game…

Instead of working with the usual grid format, I want a “free form” map where a user can place a tower anywhere that isn’t on top of the track.

I’ve got tower placement down fine, but I’m having trouble coming up with a way for enemies to move from point A to point B inside the track movie clip.

So, let’s say I have a basic long rectangle. I want enemies to start at the left side and move to the right side.

I think I can create a “pointA” movie clip and use some basic AI to get the enemies to move towards the “pointB” movie clip… but I’m not sure what I need to look into here.

I don’t need the exact code to make this happen, but rather just a point in the right direction…

What techniques do I need to look into to make this happen?

Thanks guys!