anyone knows what structure is this

i think its a well

if u put gold in it either somethin good or somethin bad happens

This is an ocean ruin, you can also check the minecraft wiki  for most if not all minecraft related things.

Yes that's a ruin (desert wells don't have chests or polished granite). It's strange to find it so... out of the water

No but there's suspicious sand in desert wells and warm ocean ruins

Warm ocean ruins are where you get sniffer eggs