While you can connect your iPad to your Windows PC via USB, due to iOS/iPadOS’s encrypted file-system, you cannot simply browse the iPad filesystem and/or transfer files using Windows Explorer.
Instead, for data and file transfer, the are two principal native methods of transferring data between PC and iPad…
1) Install iCloud for Windows on your PC. This will allow you to simply share and transfer your photos and files via iCloud.
Download iCloud for Windows – Apple Support
Set up and use iCloud for Windows – Apple Support
2) Install iTunes for Windows on your PC. This provides other file transfer and management options.
Download and use iTunes for Windows – Apple Support
You can install and use both on the PC. They will happily coexist - and provide considerable flexibility in how you move/share/transfer photos and other documents and data between iPad, iPhone and your PC.
For music derived from CD or non-Apple sources, you’ll first need to import (or “rip” from CD) this material into your iTunes Music Library - and then synchronise the Library with your iPad.
The reason for this intentional limitation, deliberately imposed by Apple, is to protect Copyright. In the case of iPadOS/iOS, Digital Rights Management (DRM) prevents direct copying of copyright material between devices. This is intended to prevent the creation of illegal copies of potentially copyright material.
The iTunes Application on your PC/Mac maintains an authorised copy your media - whether this material is loaded from a CD, or downloaded from the Apple iTunes Service - and media derived from this library can be transferred to your iThings.