Once you've connected applications through Highways, you'll be able to setup your first sync.
Navigate to Syncs
Click "New sync"
Give your sync a Name
Select the source system for your sync
Select the destination system for your sync
Select what data object you want to sync
Select when you want that data to sync
Click Create (This will not set anything live)
Once you've created your sync, click Edit
Decide on the additional settings
Click Enable to set your sync live
By clicking create, you are not setting your sync live
You can setup rules for your sync to limit when and how syncs happen