Unfortunately at the moment Musing does not support Markdown and/or HTML codes.

I tested this one weeks ago when I started posting answers as blog posts at least 2 times a week  to somehow encourage some of my followers to check out Musing. Normally I "justify" my paragraphs and center the images on my posts. That's when I noticed that Musing does not support Markdown and HTML codes.

Seeing as how the Musing development team actively listens to what their users want to overall improve this platform, I think that they will eventually add that feature soon. 

It is worth to note though that when you are on desktop or when you change your mobile view to "desktop view", you will see some of the basic features like Bold, Italic  and posting a photo.