Google Plus is the new social networking service introduced by Google. If you have got Google+ invite and want to invite some more friends and family members of yours then you can send the Google Plus invitation by the following ways.
Send invites link in sidebar
When you login to your Google+ account, you will find the following invite people to join Google+ link under Send invites section in the sidebar
On clicking the Invite link, the following Invite people popup would appear where you can enter email addresses of people you would like to add to your Google Plus circle. After entering the email addresses, click the Invite button.
Find and invite Section
The other alternative way to invite people to join Google+ is through Find and invite available as part of Google+ Circles
Drag the friend or the family member whom you want to add to your Circles. If they are not already using Google+ then you would notice an invite at the bottom left corner of the page as shown below.
Clicking the Invite link would display the Invite people to join on Google+ popup window with their email addresses.