Unsure what all this pronouns stuff means? Here's a small guide that hopefully will help getting you started.
What are pronouns?
Pronouns are part of our everyday language, and constitutes a whole part of someone's identity. Just like you call people by their name, when it's time to substitute their name for a pronoun, you should use this person's pronouns. Everyone has pronouns, aligned or not with their gender, and using the correct ones is important.
What does "x/y" means?
For single pronouns like he/him or she/her, these are quite straightforward. However, some people may have multiple preferred pronouns, in which case PronounDB will use a compact form of compound pronouns.
Here's an example: if one person goes by the pronouns of she/her or it/its, PronounDB will show this as she/it.
What's the difference between "x/y" and "y/x"?
Generally, it is an order of preference. Someone going by "she/it" is fine having either set applied on them, but prefers in this case "she". If it was "it/she", it'd be the opposite.
Beware, this is not a generality. Some would want to be called a bit of both, some simply don't care and don't prefer one over the other and just like both sets equally. Make sure to ask if you're unsure!
Pronouns.page's popular pronouns list page is a great resource and includes information about how to use pronouns.
Tip: PronounDB's compound pronouns are expressed as x&y on pronouns.page. e.g.: PronounDB's she/it would be she&it on pronouns.page.