I don't have Inbox yet, but I don't think everyone gets invites immediately. Anyways, here's some info:
> Once you have an invite, you can hover over the red create button and you will see a gold ticket - Invite to Inbox. Select that to enter your friend's email address and send the invitation.
> Quick note: if you received an invite from a friend today, your 3 invites to share won't be available until this Friday.
Note for non-Indian readers: "Auto" here is "autorickshaw", the ubiquitous (and cheap!) rickety three-wheelers that zoom about in all of India's cities. And the current official starting fare in Delhi is indeed Rs 25 for 2 km!