There's a wide variety of items that you can add to Wakelet, and most can also be added in the Android 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 notes, images, tweets and bookmarks from inside the Wakelet app. Just open a collection and click the '+' button in the bottom right, then choose an option. See the screenshot below.