Creating and editing a contact
The fields, linking a person to companies, and what changes when the record also lives on your phone.
Contacts, then New.
The fields
A name, and then as much or as little as you have: emails, phone numbers, addresses, the organizations they belong to, notes.
Only the name is genuinely required. A contact with a name and a phone number is a useful record; waiting until you have everything is how people end up with contacts in their head instead.
Linking to organizations
A contact belongs to one or more organizations, with a role at each. This is what makes them reachable from a project, and what tells you in a year's time why you have their number.
Editing
Straightforward, with one thing worth knowing: if you use the phone sync, an edit here reaches your phone and an edit on your phone reaches here. There is no "push" step; it happens on the sync's own schedule.
That also means a contact edited in two places at once resolves the way any sync does, so it is worth not doing that deliberately.
Deleting
Deleting from Steerd removes the contact.
Deleting the same person on your phone does something different: it archives them here, keeping their links to projects and invoices. That asymmetry is deliberate, because a phone is a device people tidy carelessly and a business record is not.