The personnel section is the human resource section of the game. This is the place to be to see your current drivers & staff, and to hire new members.
On the drivers page you can also set the driver roles and change the lineup. The staff page also allows you to change the roles, so that you can define who the heads are of each department. It also allows you to hire personnel who are the people working on the plans/parts/deals. If you want to take a look at new persons for your team, then you should visit the job market page. This page allows you to query the person database, and allows you to take a detailed look at each profile.
If you want to do a more advanced search for new persons then you can set this up on the scouting page. The scout can try to find out the attributes of every person.