This is a guide to all the formatting you can do on Discord, going from basic to more advanced. You can often combine different aspects of what is shown below. Given it would be awfully complex to list all combinations, I did not include them here, but feel free to play arround a bit in a private channel. If you have any questions or something is left unclear, feel free to leave a comment.
Also remember this guide only focuses on the markdown capabilities inside regular messages. While markdown in embeds should be the same I can't guarantee that it is. I will not help with any embed issues. If you want to learn more, have a look at the Discord Developer Documentation.
Keep in mind that this guide is specific to Discord markdown. Other markdown implementations my vary in syntax.
*Italic Text*
→ Italic Text**Bold Text**
→ Bold Text