Once you have received your Google+ invitation simply scroll down and look at the right bottom corner of the menu. Google+ homepage is very similar to Facebook and you will have the same 3 column interface on the homepage.
Use “Send Invitations” feature to invite your friends to Google+ and form google circles 
I Dont Find Send Invitations in Google+ ?
If you dont find Send Invitations option in your right side of Google+ homepage then you have to wait for some time to let google enable it. As they mentioned, its completely a limited Trial edition and we have to wait for sometime before they roll it out for complete access.
Another Alternative Way if you Dont find “Send Invitations”
click “Share” on the top right corner… Type a content -> include the Circles and also email u want to invite… click share. accept the “Okay, Got it” button. Click Share again… Ur friends in circles and email ID’s will receive the invite…
Download Google+ iPhone App
Apple has approved an iPhone, iPod Touch and iPad App of Google+ few days ago and here is the link to download Google Plus iPhone App.
