Find an Ocean Ruins or shipwreck
Search the shipwreck for a Treasure Map chest
Take the Buried Treasure Map
Open the map and locate the red X
Travel to the marked beach or shoreline
Use the map to align yourself with the X
Dig down at the X location
Look for the buried treasure chest underground or under sand/gravel
Use a shovel to dig faster
Open the chest to collect the treasure
Repeat with more treasure maps if needed