To start a new post, simply click on the box that reads "Create a New Post". Enter in your title.
Notice the three icons below the title.
The first icon is the Media Hub, where you can upload images, videos, and GIFs to add to slides in your posts. .
The second icon is the Text Editor. You can use this tool to add text in your slideshow.
The third icon is the Line Tool, leave that alone for now (it's glitchy).