You can reinstall an already purchased Android app so long as you’re still using an Android device and you’re either:

• Signed into the Google Play account that purchased the app
• Signed into a Google Play account which is a member of the same “Google Play Family Library” that the purchasing account is a member of and the purchasing account has shared the app with that “Google Play Family Library“

To reinstall an Android app you purchased using the email you are yourself signed into Google Play with, simply visit the app’s store page within Google Play and tap the “Install” button – if you’re prompted for payment, check you’re signed into the appropriate Google Play account

To install an Android app shared with you via a “Google Play Family Library“, tap the “menu” button (three short horizontal lines) in Google Play and select “Family Library” then select the app.

Note: Android apps can’t officially used on Windows or Mac PCs, though some third party systems (such as, without any implied warranty, BlueStacks) claim to be able to run Android apps on Windows PCs.