In Sequences, choose New sequence and give it a name — this is an internal label; recipients never see it.
On the sequence page, add steps and drag to reorder them. For each step, pick a channel and its content:
Set a delay on each step to control how long to wait before it sends.
Open the sending panel to choose the sending mailbox and domain, and optionally set a timezone-aware schedule so steps only send during the hours you choose.
Work through the launch checklist (it flags anything missing), then activate the sequence.
Steps stay editable even after activation. Editing a step creates a new version, and any contact already mid-sequence stays on the version they started on — so improving a live sequence never disrupts people already moving through it.