When you received an invite from a partner company you will get an email that says "Global IT" wants to connect with your company.
To respond to the received invite follow the steps:
Go to Network -> Partner Network in the sidebar.
Change the status in the filter at the top right to "Invite received"
Click " Respond to invite" if you wish to connect with the company.
If you wish to see the companies that you are connected with change the status to "Connected".