To the Android Market? Go to http://market.android.com/publish with your developer account (you will need to pay for one at $25 - this helps reduce spamming of the Market). Your app will need to be exported as an APK signed with your private certificate, and zipaligned to 4 bytes, otherwise the Market will reject your app. Debug mode should be turned off. Your app should be versioned. Of course all this is in the Android Developer Guide:
http://developer.android.com/guide/publishing/versioning.html
http://developer.android.com/guide/publishing/preparing.html
http://developer.android.com/guide/publishing/app-signing.html
http://developer.android.com/guide/publishing/publishing.html
Upload to a website? Use FTP.