Hi @Sha_Hassan welcome,
Start here: https://shopify.dev/custom-storefronts
Your asking things on a BROOOOAD and DEEEEEP topic you will want to browse around to have an idea of what resources are available
Then work your way down. https://shopify.dev/api/storefront
If your a partner create a test store.
Install shopifys graphql tool for the storefront api https://shopify-graphiql-app.shopifycloud.com/
And use the example demos like hydrogen
https://github.com/Shopify/storefront-api-examples
In the dev docs, if a page is confusing there is a feedback button at the bottom of each page, for example on https://shopify.dev/api/examples/cart I left feedback that is not clear how discounts are used in creating a cart.
Then will this also update the inventory?
Yes in the shopify admin
manage refunds?
Ambiguous what ever "manage" means. In general merchants staff manage such things in the shopify admin, if your building a custom backend for staff then that's the admin api you need to look at not the storefront api.
payments will be through shopify?
Yes through the web checkout which uses the stores payment gateway
and how can we use discount codes?
Through the storefront api to use
https://shopify.dev/api/storefront/2022-04/mutations/cartDiscountCodesUpdate
To create https://shopify.dev/api/examples/discounts
Beyond that you really want to
- research existing topics the forums for each bullet point individually. Glooming them all together just makes for over complicated discussion that can become overwhelming.
- And dig through the docs, api reference and tools&examples a bit more as some of these questions are very broad and desired outcomes can be subjective.
Like what "manage refunds" means if your not already experienced with shopifys admin but have some other unspoken expectation for what that "manage" means.
You'll only know for sure by making and testing that process with some demos.
