As an employee, you will be invited by your employer to 'join' their company.
You will receive this invite via email and it'll look similar to the following:
All you need do is click on the Accept button in the email and you'll be taken to the registration page.
Registration is free so add your relevant details and then follow the instructions.
It only takes 2 seconds, and once registered with your employer's company you'll, first, complete your personal profile, and then your employer will assign you to the relevant project/tasks.
Refer to the employees section of the knowledge base for information on how to manage actions, view assigned projects, etc.