To give a bit more tailored advice, the gender variables you use depend on the genders you plan to offer. Standard afaik is male, female, and non-binary. How you set up variables is entirely dependent on your writing style. Here’s my bare minimum, which comes from an example given to me by another user whose name I can’t remember.
*create g 0
*create plural false
*create he ""
*create him ""
*create his ""
*create himself ""
I use g as a numeric variable for a few reasons. It allows me to have three gender options, and it also makes it easy to use multireplace. For example:
"I just want to spend time with @{g you and the girls|you girls|you and the girls|}," Christine replies.
plural is used to change references when using “they/them” pronouns. For example:
"I think ${he}@{plural 're|'s} the worst," Parker mutters.
he, him, his, and himself are my most common references, so I use string variables and set them when the player decides their gender. I also sometimes use boy and guy. I’ve added the pronouns I replace the strings with depending on gender in the summary. These typically cover everything you’ll ever need.
Summary
Male: he, him, his, himself, boy, guy, boyfriend, husband
Female: she, her, her, herself, girl, gal, girlfriend, wife
Non-binary: they, them, their, themself, kid, person, partner, spouse
You don’t have to name your variables the way I did. I choose to use male pronouns as the variable names because it let’s me consider grammar while I’m writing. My brain doesn’t process true gender-neutral variable names like xe and xim because I don’t really see them as words.
If you’re looking to be more inclusive, you could also let players set their own pronouns by using *input_text for all the pronoun variables. This requires a bit of extra coding but some players appreciate it.