You would add Assigned Activity Nodes to the Workflow and check the Send Notification checkbox. Ideally, the Users that need to sign off can be populated from a Context Team Role (you'll need to add that Role to the pbo (primary business object) Team, and you would use that Role as resource pool for the Assignment. Also set to "All" Required (any will complete when any one assignee completes).
You may need to enable Digital Signatures. I advocate for a "your login is your signature" approach so do not have Digital Signatures enabled. If you do have Digital Signatures enabled, there is an option to set that as a requirement for the WF Assigned Activity as well.
If the sign-off users are variable, you can make an upstream assigned activity a Set Up Participants task type (allowing an upstream participant to set downstream signers). You can also use a Group as a resource pool for an assigned activity.