You need to mount the disks or partitions that you want to use to a folder (mount point) before the data within it is accessible to you. From there you'll be able to navigate the filesystem and perform read or write operations.
You can manually mount disks and partitions manually each time you need to use it or you can add an entry in /etc/fstab so it automatically mounts everytime your system boots. You can mount these drives via the device name, label or UUID.
$ lsblk NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT loop0 7:0 0 55.4M 1 loop /snap/core18/1944 loop1 7:1 0 55.4M 1 loop /snap/core18/1932 loop2 7:2 0 217.9M 1 loop /snap/gnome-3-34-1804/60 loop3 7:3 0 219M 1 loop /snap/gnome-3-34-1804/66 loop4 7:4 0 64.8M 1 loop /snap/gtk-common-themes/1514 loop5 7:5 0 51M 1 loop /snap/snap-store/518 loop6 7:6 0 62.1M 1 loop /snap/gtk-common-themes/1506 loop7 7:7 0 51M 1 loop /snap/snap-store/498 loop8 7:8 0 31.1M 1 loop /snap/snapd/10707 loop9 7:9 0 31.1M 1 loop /snap/snapd/10492 sda 8:0 0 20G 0 disk ├─sda1 8:1 0 1M 0 part ├─sda2 8:2 0 513M 0 part /boot/efi └─sda3 8:3 0 19.5G 0 part / sdb 8:16 0 20G 0 disk └─sdb1 8:17 0 20G 0 part sr0 11:0 1 1024M 0 rom
$ blkid /dev/sdb1 /dev/sdb1: UUID="ccab0f8d-3b5b-4189-9da3-23c49159c318" BLOCK_SIZE="4096" TYPE="ext4" PARTUUID="c088a647-01"
$ mkdir disk
$ sudo mount -t ext4 /dev/sdb1 disk [sudo] password for user:
$ df -h Filesystem Size Used Avail Use% Mounted on tmpfs 391M 1.8M 389M 1% /run /dev/sda3 20G 7.1G 12G 39% / tmpfs 2.0G 0 2.0G 0% /dev/shm tmpfs 5.0M 0 5.0M 0% /run/lock tmpfs 4.0M 0 4.0M 0% /sys/fs/cgroup /dev/sda2 512M 7.8M 505M 2% /boot/efi tmpfs 391M 112K 391M 1% /run/user/1000 /dev/sdb1 20G 45M 19G 1% /home/user/disk
$ sudo umount /dev/sdb1
$ sudo vi /etc/fstab
/dev/sdb1 /home/user/disk ext4 defaults 0 0
$ sudo mount -a
$ df -h Filesystem Size Used Avail Use% Mounted on tmpfs 391M 1.8M 389M 1% /run /dev/sda3 20G 7.1G 12G 39% / tmpfs 2.0G 0 2.0G 0% /dev/shm tmpfs 5.0M 0 5.0M 0% /run/lock tmpfs 4.0M 0 4.0M 0% /sys/fs/cgroup /dev/sda2 512M 7.8M 505M 2% /boot/efi tmpfs 391M 112K 391M 1% /run/user/1000 /dev/sdb1 20G 45M 19G 1% /home/user/disk
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