Mounting makes a filesystem available at a directory path. Linux can mount internal disks, USB drives, network shares and disk images, but the exact command depends on the device and filesystem type.
Find the device
lsblk
blkid
Identify the correct partition before mounting. Do not guess device names on systems with important data.
Create a mount point
sudo mkdir -p /mnt/data
Mount the filesystem
sudo mount /dev/sdXN /mnt/data
Replace /dev/sdXN with the actual partition, for example /dev/sdb1. For NTFS, exFAT, NFS or SMB shares, extra packages or options may be required.
Unmount safely
sudo umount /mnt/data
Unmount removable drives before unplugging them to reduce the risk of data loss.