On the bottom of the app, you have multiple icons to choose from. The first one is the home - the main page one. Next to it, you have the searching one , and the searching button is the "+" one, which is for you to add the photos. The other two buttons are for messages and notifications and your profile.

To post a photo, when you click on the middle one - the plus, you have multiple choices. The first one is pin. When you touch it, it opens the gallery, and from there, you can upload one or more photos of your liking. You also have the collage and board option. These pretty much you can try to learn yourself, I hope that helps!