Use the # character to indicate a heading line:
You can customise the size of headings, as well as their color (and the color of the # symbol itself) from Soulver's styling preferences. There is also an option to strip heading symbols when exporting into PDF or printing.
If you want Soulver to ignore numbers or calculations, put them inside a comment (indicated by two slashes):
You can also add comments on the end of lines:
I spent $128 + $45 on clothes // on 10-02-2019 | $173.00
Hint: If there's a single number you want to exclude from an expression, you can also put it in parentheses, like this:
$699 (for iPhone 12) | $699