Every place Abraham went, he dug a well, built an altar and put up a tent.
They were places Abraham worshipped God, and he wanted to remember the way in which God met him in that place. When he left that location the tent would come down and go with him, but the well and the altar would remain as a memorial.
His son Isaac came back to those places.
Isaac re-dug some of the wells his father had made because the Philistines had filled them after Abraham’s death.
Other places, he built a second altar and dug a second well because he called on the name of the Lord God and had his own experience with God.