system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How are oil drilling platforms and wind turbines built in the ocean? How are they stable?
gpt
They stand on pretty solid legs that are buried into the seafloor. 

Water current is stronger than wind, but with thin but strong steel constructions thats not a much bigger issue than building a tall building on land.

For bigger depths there are also concepts with floaters and ropes connected to anchors.