When you have more than one members in To Be Invited status you can use the Quick Tasks box to send invites to all of them at once. 

1. Make sure you're on the All Member Records tab, click Send Invites, and follow the prompts.

When you want to send invitations to only specific members: 

1. Select the members' checkbox whom you'd like to invite, click Message MembersInvite, and follow the prompts. Hint: use Advanced Search and Filter to quickly find your members.