Once you have reached the Modern Age you will be able to start searching for a new planet to inhabit. You can begin this process by creating an Observatory, you will then be able to start looking towards the stars and learn their basic info
Once you have found a suitable planet you can create a [Rover] to go to the planet and start gathering useful data.
The Recon Rover is optional but can be extremely important. Because you may never know what is on a planet and sending astronauts that aren't correctly equipped may result in their unfortunate deaths
Once you feel you have sufficient information you can either send in a team of astronauts or cow astronauts. You are able to send the cows to the planet through use of the Cowtivo Skycraper. If you choose to send the cows to the planet, they will begin to wander around, proving if the planet is habitable or not. But there is the chance that the cows could evolve and take over the planet, leaving you to eliminate them to have the planet. If you choose to have the astronauts go instead, then they will travel to the planet and begin to explore. If the planet does not fit certain conditions for normal life, you can terraform the planet by adding special or buildings or by adding trees (if there isn't enough oxygen.)