hello , how can i download my i cloud back up to my pc ???

What do you mean 'download my icloud storage', what do you want to download ? An iCloud backup can be restored onto an iOS device (so if you login to the same account on an iOS device then you can restore that backup onto it), it can't be downloaded onto a computer.

If you want to redownload some your past purchases then what you can redownload will show under the Purchased link under Quicklinks on the right-hand side of the iTunes store homepage on your computer's iTunes.