dnd 5e – How do runes work in D&D 5e? Can a Rune Knight forge them?

One of my players, new to D&D, is playing a Rune Knight, but in his background he’s a son of merchants, and he asked me if he can produce runes to use or sell. Now, I’m aware that from the Rune Knight’s class features there is nothing of the sort, but it does grant proficiency with smith’s tools, so he wanted to know if it would be possible for him to create simple runes. I have my doubts on this, because he’s no spellcaster and usually you need to know the spell to write a scroll of it, but the Rune Knight is affine to the rune magic indeed.
So I wanted to ask: how do runes work in D&D 5e? And, if this isn’t already included in the answer to the first question, could a Rune Knight inscribe one? How, and with what costs and times?