You need to create private APP and it will generate API and SECRET keys. Using that you will be able to do REST API requests.
Please note that you will require to host code somewhere which work as middleman between front-end and back-end.
Welcome to the community. I would start with reading the developer documents. There is more than one way to do any of the following.
Run code on a storefront: https://shopify.dev/docs/admin-api/rest/reference/online-store/scripttag
You'll also need App Proxy to securely transfer that data: https://shopify.dev/docs/app-extensions/extension-areas#online-store
Storing and updating in Shopify: https://shopify.dev/docs/admin-api/rest/reference
Wish you all the best,