How do you use two hdd at once?

To use two HDDs at once, you can either configure them as separate drives in your operating system, allowing you to store and access data on both independently, or set them up in a RAID configuration for improved performance or redundancy. For independent use, simply connect both drives to your computer and ensure they're recognized in the BiOS/UEFI. For RAID, you may need a RAID controller or software that supports this configuration. Ensure to back up data before setting up RAID, as it may involve formatting drives.