Tools › Feature graphic maker (1024 x 500)
Google Play will not publish a listing without a feature graphic: a 1024 x 500 banner at the top of your store page. Type your app name and one line about it, pick your colours, and download it.
It is shown small, and often partly covered by a play button when you add a promo video. Keep text large and near the centre, use at most one line besides the name, and avoid putting "Download now" or ratings on it: Google treats those as misleading metadata.
1024 x 500 pixels, JPEG or 24-bit PNG without transparency.
Yes, for every app on Google Play.
Only if it reads well at small size. Website heroes usually carry too much text; a simpler version works better.
Turn your website, HTML or ZIP into an Android app first: build it free, with the APK and the Play Store AAB.