My washer has a spinning problem, the tub seems to be unbalanced. What is that all about?

My washer has a spinning problem, the tub seems to be unbalanced. What is that all about?
Most washers will either actually "get out of balance" if you wash an usually large load or items that are large such as bed sheets, etc or seem to get out of balance. Try taking some items out/rearranging the load. At the top of the tub inside there is a ring that is filled with a jelly like liquid that assist in keeping the tub balanced. There's not much you can do other than what I've mentioned.

My washer makes a loud knocking noise when agitating . What is the source of this problem