Can you colonise other planet

Answer 1

Yes but to make the atmosphere suitable for humans to breathe without spacesuits you would have to change the chemical nature of the atmosphere on that planet, which can take a very long time.

In the short term, you could build massive buildings and seal them so that you could walk around inside without a spacesuit but you could never go outside without protection until the atmosphere is safe. Some planets don't have much of an atmosphere so you would always have to wear a protective spacesuit because without an atmosphere you would not be protected from the deadly dangerous rays of the sun. Without an atmosphere to protect you, you would get too much radiation and die.