Think if it this way. You and your friend are playing catch. If you both stand still, it’s pretty easy. If one person starts moving, you throw ‘ahead’ of that person so that the ball gets there when they get there. If you kept it the same, you’d miss them.
Now make both of you move, it gets more complicated based on how you two are moving to each other and how fast. You either increase or decrease the ‘lead’ you are putting on the ball based on those variables.
This is the general principal of ‘locking on’ a target and letting the computer figure out where to point at the beginning. The addition of self guidance means that if the target does something, you still have a good chance of hitting it because it is still pretty likely that it will be _close_ to the original solution.
TL;DR – It’s the computer making a good guess as to where the target will be when the missile/torpedo/projectile will get there and trying to hit it.
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