put out his eyes

"removed his eyes"

down to Gaza

They brought Samson to Gaza which is lower in elevation than his home.

"chained him with bronze shackles" or "tied him up using bronze shackles"

locks on the end of chains that hold a prisoner at his feet or hands, or both

"pulled the millstone around in a circle"

A large animal usually pulls the millstone around in a circle to crush grain. The Philistines humiliate Samson here.