If you land on a Property space that is currently un-owned by another opponent, you can choose to buy the property. You are then considered the Owner of the Property. As long as you own the property, it’s value will be collected each time you pass Go. All newly bought Properties are given 1 house to start. Effectively, level 1 properties. You are also immediately awarded Dollars equal to the amount of money a 1-house Cash-in would be.
If you land on a Property space that is owned by another player, you can ‘steal’ the property, and are then considered the owner. Stealing a property does not award money. However, the upgrade applied after stealing the property will award coins to the stealing player.
If you land on all color properties within a neighborhood without any other players stealing those properties; you will now have a color monopoly. Color Monopoly earns a rent Bonus for passing GO on your next Go. The Monopoly Bonus is canceled if players steal any of the properties before the next GO. You will lock-in the Monopoly Bonus automatically if you have fully upgrade both properties and lock them from property thieves.