keep away (from ~) means don’t go near (e.g. keep away from the edge of the pool. You might fall in)
keep on doing something means continue doing (e.g. Keep on stirring until the liquid comes to a boil.)
keep on doing something means do it continuously or repeatedly (e.g. He keeps on criticising me. I’m fed up with it!)
keep somebody/ something out means stop from entering (e.g. Try to keep the wet dog out of the living room.)
keep something from some body means not tell (e.g. We kept our relationship from our parents for two years.)
keep up (with somebody) means continue at the same speed or level (e.g. You’re walking too fast. I can’t keep up (with you), You’re doing well. Keep it up!)
keep up + with (e.g. You’re walking too fast. I can’t keep up with you.)
knock down a building/ blow something down/ cut something down etc. (e.g. Why did you cut down the tree in your garden?) Also be knocked down (by a car etc.) (e.g. A man was knocked down by a car and taken to hospital.)