When you click 'Register now' on an event, you will be given the opportunity to invite your colleagues using the invite box. Input their emails, add a message and submit, and it will send an email to them letting them know you've invited them.
You can also do this by clicking the 'Invite colleagues' button on the event page.
And finally the simplest way is to copy the URL of the event page and send it to your colleague directly, or forward them an event email you have received. They can then register using their own Apolitical account.
If they don't have an Apolitical account, they will need to make one to register for the event.