How to check block devices (eMMC, SDcard, USB storage)

To check the available storage devices run

$ lsblk -a -i -T -f
NAME         FSTYPE   FSVER LABEL            UUID                                 FSAVAIL FSUSE% MOUNTPOINTS
loop2
loop3
loop4
loop5
loop6
loop7
mmcblk2
|-mmcblk2p1  vfat           boot             2C90-B76C
|-mmcblk2p2  ext4           root             f5274060-57d8-4cc2-ae0f-51997686e138
`-mmcblk2p3  ext4           containers-unuse 5782f36e-2c0b-4912-8756-f9998e5ac8d7
mmcblk2boot0
mmcblk2boot1
mmcblk1
|-mmcblk1p1  vfat           boot             089A-78DD                              40.6M    51% /boot
|-mmcblk1p2  ext4           root             175b5016-b85f-4a8b-9a73-26b22ef62e81  214.1M    61% /
`-mmcblk1p3  ext4           containers       42a82830-17fd-4fa2-9488-eec88f5e9954   12.5G     5% /apps

To mount an unmounted device run

$ mount -t <FSTYPE> /dev/<NAME> <PATH TO MOUNT TO>

e.g.

$ mkdir -p /tmp/my-device
$ mount -t ext4 /dev/mmcblk2p3 /tmp/my-device

would mount mmcblk2p3 to /tmp/my-device. Afterwards you can access the files and folder under /tmp/my-device/.

More information

For even more specific information run lsblk -h and choose the additional information you want to see.

Persistence

Mounting devices is not persistent, those mounts will be lost after a reboot.