What does ring giving king means?

A “ring-giver” is an Anglo-Saxon term for king or overlord. To quote Beowulf:

A ring-giver (or “kenning”) was one who gives arm-rings or neck-rings (also known as torcs) of precious metals to brave warriors to gain and/or reward their service in battle.This is how political and military power worked in the Early Middle Ages: kings build up warbands by giving riches to fighting men, and then go out and conquer and plunder to rebuild their hoards of precious metals, rinse and repeat. 

When you run out of precious metals, then you start giving land away, and pretty soon you’ve got feudalism.