Not sure if this is what you want, there are several trailheads to get started with MC.
- Log in to your MC account
- Hover on Audience Builder
- Click Contact Builder
- Click on tab Data Sources
- Click sub tab Synchronised
- (if you have already connected your CRM to MC) A box with your connected user should appear. Click on it.
Here you can see all your sObjects that are connected and synced. If you dont have any or want to connect some or more then:
- click Set up Object button on the top right
Now all the sObjects that are available will appear and you can sync them. This will make them available in the MC environment.
Some will be unavailable at the moment, this is because they require others to be synced first. Once you start syncing the most basic ones, others will become available.
Hope this is what you were looking for.