I can't say I've ever shared pictures with a friend, as in my circles it would be awkward. However, I used to share her pics quite regularly on sites that would allow such things. It's a bit addictive to be honest.
I have done so also but just with selected people I have developed a good communication on other sites.
Click on someones avatar. Takes you to their home thingie. Click 'start a conversation' , title it so you'll recognize it later, then fill out the form and hit 'start'. From then on, on your opening page, by "alerts" will be a notice for "inbox", click it. Ta-dah!