It'll list all the partitions and will give you their sizes and how much space is used/available.
I hope this helps.
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Better still, use "df -h" option it will lists the mounted disks in mb size, used, available, capacity, mounted on, .... and if you want to see other options for "df" just type "df --help" (2dashes and help)
and it will lists all the options available for df command.