From the mesh list, click the Sharing button next to the one you want to share.
From here you can see anyone that the mesh is already shared with:
And then click the Add Members button in the top right to add new people:
Just enter their email addresses, each one on a new line.
If you subscribe to Usermesh you can automatically send an email to the member to let them know that they've been invited. This can also include custom invite text:
