To summon a mount, open your Collections tab (default hotkey: Shift+P), and click on the Mounts section. Here, you can browse your available mounts and either drag them to your action bar or set them as your favorite mounts. To summon a mount from your action bar, simply press the corresponding hotkey. To summon a random favorite mount, you can use the Summon Random Favorite Mount button in the Mounts section of your Collections tab.