Child theme jquery

i created a child theme in antimatter. my custom js is working .when i use just js codes it is working.but when i use jquery in my custom js it is not working.what must i do?where must i place my jqury.js file?

Also replied in Gitter. Is jquery loaded in the page? Antimatter loads it this way https://github.com/getgrav/grav-theme-antimatter/blob/develop/templates/partials/base.html.twig#L33

thank you :)