how to use extended partion on ext3

I have got a new ubuntu server, which I can access as root: and I can see the following partitions.

/dev/sda1  *          2048     782335     780288  381M 83 Linux
/dev/sda2           784382 3907028991 3906244610  1.8T  5 Extended
/dev/sda5           784384 3856726015 3855941632  1.8T 83 Linux
/dev/sda6       3856728064 3907028991   50300928   24G 82 Linux swap / Solaris

but when I use df -h I can see it like this:

Filesystem      Size  Used Avail Use% Mounted on
udev            7.9G     0  7.9G   0% /dev
tmpfs           1.6G  169M  1.5G  11% /run
/dev/sda5       1.8T  6.8G  1.7T   1% /
tmpfs           7.9G     0  7.9G   0% /dev/shm
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs           7.9G     0  7.9G   0% /sys/fs/cgroup
/dev/sda1       361M   54M  289M  16% /boot
tmpfs           1.6G     0  1.6G   0% /run/user/1000

My question is how can I use /dev/sda2?

I tried like this:

root@server2:/# sudo mount /dev/sda2 /media/backup

but get this error:

mount: wrong fs type, bad option, bad superblock on /dev/sda2,
       missing codepage or helper program, or other error