No problem downloading, but despite extensive backpacking experience I can’t decipher half of these! (E.g., toilet paper roll or marshmallow?)

You just have to figure it out sans instructions. I'll try to help -- but first, it only works in iMessage. Once you open iMessage, go to any conversation you already have started and click the icon that looks like the App Store icon. Once you're in there, press the icon at the bottom left that looks like four ovals arranged in a square. In the resulting screen, click the +Store icon, then click the Manage button at the top and either click the slider for "Automatically Add Apps" or find "Campmojis" and click the slider to enable it.

Reviewers who can't find the emojis: This is a sticker pack for iMessage. To find them after downloading, go into messages, click the button next to the text bar (kind of looks like an A) and click on the 4 dot icon at the bottom left. Then click on store, then manage. All your stickers should be there, including Campmojis. Found mine fine after downloading. If you can't find them, you don't need to be texting anyway, just call people.

I found the directions for how to use the stickers in the iMessage app, however, the app does not appear on my phone anywhere. The "cloud download" icon is showing next to the app name in the App Store.