To send an invitation, you can click on Add user > Invite users.Enter emails you want to invite separated with coma. After validation, an email is sent to this address. Your colleagues will have a link to signup and join your company.
Create user account
You can create directly accounts for your colleagues. For that, click on Add user > Create account. After giving email, name and Role, you can specify a password (or generate a random one). You just have to send credentials to your teammate.