Go to www.tinkercad.com
Using Social Providers
Click on Learn (top right hand corner)
Complete all the Direct Starters -- there are seven of them
Size it up!
Click on Learn again (top right hand corner)
Click on See All Projects
From here you can select the type of Space Station Project you want to complete. Build a rocketship, Build a housing module, Build a research pod.
Once you know how to build some modules, go ahead and construct your entire Exoplanet Colony. To build your colony, increase your GRID size to 1000 x 1000 (you do this in the bottom right corner of your grid)
Do some research about the types of modules you might need (crew quarters, energy production, waste management, greenhouse, etc