I want to purchase music from iTunes on my laptop

For instructions on buying iTunes music on a Windows PC, see the following from: Buy music from the iTunes Store - Apple Support

Buy music in iTunes on your PC

1. Open iTunes.
2. Choose Music from the pop-up menu, then click Store in the navigation bar.
3. Find the song or album that you want to buy.
4. Click the price next to the song or album to buy it.
5. Sign in with your Apple ID and password to complete the purchase. Need help?

After you buy music, you can find it in your music library. 

To download music to listen to offline, click the Download button  next to a song or album.