How to use 'go' and 'come' correctly

Both words involve movement from one place to another. The only difference is the direction.
When we go from A to B, we set off from a near spot to somewhere far away from us. On the hand, when say to someone, "Come here, please.", we expect him to move from his place far away to the spot near us.

Some examples of the usage of both words are as follows:
a) I usually go to the shop at the end of the road to buy food.
b) Please come to my house if you are free.
c) If you come here awhile, I will go with you to the place.