People are added in HR → Directory, either directly or imported from your accounting software if they are already set up there.
Importing avoids typing the same records twice and keeps names and pay consistent between the two systems.
What to record
Department, which is how costs group later.
Pay basis — an annual salary or an hourly rate. This is what makes labour cost per job answerable at all; without it, jobs get costed for materials and not for time, which reliably makes every job look more profitable than it was. See job costs.
Employee or contractor. This changes tax treatment, what you owe, and what you are liable for — see employee or contractor, which is decided by how somebody actually works rather than by what the paperwork says.
When someone leaves
Mark them inactive rather than deleting them. Deleting removes their history from the jobs they worked, which means last year's margins change when this year's staff list does.
What follows
Certifications and signed paperwork go in employee documents, which tracks expiry. A first week runs from onboarding.