The CD isn't actually necessary - that's the good news. Canon's pretty solid about keeping driver support available online even for older models, so you're not stuck at all. Just head to Canon's support website, search for your MG2500 model, and download the drivers for your specific operating system (Windows or Mac). Once you've got the installer, run it and follow the prompts. When it asks how you want to connect, make sure you pick USB. Then plug in your printer with a USB cable and let the installation finish. Windows or Mac should detect it during setup.
If you want to skip the driver download entirely, some older Canon printers will work on a basic level just by plugging them in - your OS might recognize it as a generic printer without any fancy features. That usually means you can print, but you won't have access to scanning or any of the Pixma software. Honestly, grabbing the actual drivers takes maybe five minutes and gives you full functionality, so it's worth doing it properly. Just make sure you're downloading from Canon's official site, not some random third-party source.