Before creating a sequence from scratch you'll want to check out our 'Create from Template' option, pictured below. This will save you some time. More on that here.

When creating a new sequence from Scratch (click Marketing > Sequences > click the dropdown menu to the right > Sequence from Scratch).

You'll notice the Trigger and Counter Conditions are set on the first page. The Action will be set on the next page.

Actions are added by using the 'Add Step' button, allowing you to map out what happens next.