Sharing a page works via the Send page link in the top right corner of your page.

You will be presented with a dialog where you can choose users from your Confluence, enter any email address you like or share the page with a whole user group. 

Users and groups can be chosen from a drop down, email addresses have to be confirmed with a click on the + add link. 
If you chose a wrong user, email or group, you can delete it with a click on the x.

Share your page with Send when you're done.