Summarize the following:
This is the app with the rainbow pinwheel icon and can be found in the app drawer.  This it the 3 dots connected by lines in the lower left corner of the screen. Scroll down if you do not see it in the list of options. This is the blue arrow in the lower right corner. A blue checkmark will appear next to a name when it is selected. This is the blue arrow in the lower right corner. The photo will be uploaded and sent as a snap to the selected contacts.

Summary:
Open the Photos app. Tap the photo you want to upload. Tap the Share button. Tap Snapchat. Tap the Send button. Select recipients. Tap the Send button.