Wreck: to destroy or smash up, as in a shipwreck, or if you are American, a car wreck. It can also refer to something that has already been broken up. 'It's an old wreck.' It can also refer to items brought ashore after a shipwreck.
Wreak: cause a lot of damage. Pronounced 'reek'. 'Page planning have wreaked havoc on page three.' 'The damage wreaked by that woman ruined my wedding'. NOTE: Every time you write 'wrecked havoc', your chief sub kills a kitten.
Rack: this is a framework for supporting things, as in a luggage rack. You can rack up points in a game -- or rack up trade deals or successes. It is also an instrument of torture -- so someone who is on the rack is probably being dragged over the coals as they receive a bollocking.
Wrack: Seaweed; or thin high cloud.
Here's where it gets complicated. A rack for holding things is never spelled 'wrack'; The seaweed is never spelled 'rack'; however, you can rack, or wrack, your brains when thinking hard; and be racked, or wracked, with guilt. Something falling into disrepair can go to 'rack and ruin' or 'wrack and ruin'. And a diaphanous wrack, or rack, of cloud can cover the gibbous moon.