I have an existing app already on the app store... I want to upload a new app to the app store but its asking for a bundle ID? Can I use the same one I used for the first ap
You will need to create a new bundle ID. Please see Apple's documentation, "iTunes Connect Developer Guide"
iTunes Connect Developer Guide
Specifically, the Bundle ID needs to be unique for each app. You will also need a new iTunes connect profile. It is, unfortunately, a complicated process.