After you are logged, on the left side menu you can click on "Referrals", which shows you options on how you can invite your personal network.
Two ways you can invite someone:
1. Import your contacts from an online address book (google, outlook, yahoo or apple):
As an example - If you click on the button "Google" - it will take you to authorize your google account to load up all your contacts from Google/Gmail.
Once, authenticated you will be able to see all your contacts. Simply select the particular contact or multiple contacts that you like to invite and they will receive an email with your invitation to join the network.
2. There is an alternate way to invite your connections by manually typing their email.
On the same Referrals page, you will see an option "Enter Your Contacts", when clicked opens up a placeholder, where you can enter your contacts. Here you can enter all your contacts separated by comma and invite.
Enjoy helping others to find an opportunity :)