There's a wide variety of items that you can add to Wakelet, and most can also be added in the iOS app as well. 

Most things that have a 'Share' button, like articles in your mobile browser, tweets in the twitter app and images from your photo gallery can be shared straight into the Wakelet app.

You can also add links (by copying and pasting), notes, images, tweets and bookmarks from inside the Wakelet app. Just open a collection and click the 'Add an Item' button at the bottom, then choose an option. See the screenshots below.