Very simple.

Some familiarity with the setting is helpful (mainly for generating a concept), but not necessary.

I am not putting restrictions on whether people apply with a full character sheet, or only a brief concept.

There are really two (okay three probably) things to consider.

1. Soulbound are not beginners. They have a combination of training, skills, and experience that make them stand out. What this means is for background, you are probably long past the "grew up on a farm" origin point.

2. They often have a defining moment. Something they can point to and say to a god, "This is why I should be a Soulbound!" Which leads me into no. 3

3. To be Soulbound, a god has to approve. Which God approved yours (and possibly why)?

This is MY distinction, and I know the game allows other options. I have a whole rant on why I think these are bad. So for the intent of this game, your binding was approved by a god.