How do I create a custom payment plugin for Shopify?

Payments + Shipping & Fulfilment
1

I’m looking to build a simple Shopify payment plugin, where during checkout customers can select our payment method and will be redirected to our gateway for the payment. On successful payment will be redirected back to a “Payment Complete” page. We would like to collect the product/s data as well if possible. My team and I are complete beginners to Shopify app developments any help will be appreciated.