I suggest you start with Leaflet, e.g. using sentinelhub-py:

GitHub - sentinel-hub/sentinelhub-js: Download and process satellite imagery...

Download and process satellite imagery in JavaScript or TypeScript using Sentinel Hub services. - GitHub - sentinel-hub/sentinelhub-js: Download and process satellite imagery in JavaScript or TypeS...

Perhaps check Sentinel Playground’s source code as well:

GitHub - sentinel-hub/SentinelPlayground: Simple application for using...

Simple application for using Sentinel-2 WMS service - GitHub - sentinel-hub/SentinelPlayground: Simple application for using Sentinel-2 WMS service

@gmilcinski Thanks for your assistance!

I will follow up with the guides above.

If you have time, look at this link. Basically it is a crop monitoring platform and I wanted to develop only the part to import/upload shapefile or draw polygon and also extract NDVI values. Can I do that without having to download the images, or is there a way I would simply do that?

Thanks!

Well, you will need to do an app for an user to draw the polygon. Once you have it, you can simply use this request and get NDVI values:

Examples for S2L1C

Use these CURL and Postman examples to access Sentinel-2 L1C data with Sentinel Hub Processing API.

or, if you prefer picture:

Examples for S2L1C

Use these CURL and Postman examples to access Sentinel-2 L1C data with Sentinel Hub Processing API.

Thanks @gmilcinski for the prompt response.

Does that mean I will have to develop something like a web app, or more a web page that will have all of my parameters?