When you are posting a new note or comment you can use Markdown syntax. Since Pumpa version v0.8.4 inline HTML is also allowed as in standard Markdown.

For example:

• *stars* make the word emphasised, typically italics
• **double stars** strong emphasis, typically bold
• surround links with < and > like so: <http://example.com/>
• link text [like this](http://example.com/)
• a hash (#) at the start of the line makes an H1 heading, so be careful with hash tags

Enable the Preview below the text editing window to see what the output will be before posting it to pump.io.

For the full Markdown syntax see John Gruber's page.