How to mount partition from disk

You can't. That's not an actual partition, it's an "extended" partition. These are special partitions that only exist to contain other partitions. They are a trick to allow more than the maximum number of logical partitions the classic MBR partitioning scheme can understand.

In your case, your extended partition sda2 contains two logical partitions: sda5 and sda6. You have both of these mounted, one at / and the other as a swap partition. There's nothing left for you to mount.

You can't ! /dev/sda2 is an extended partition that contains /dev/sda5 and /dev/sda6.

You can (if the Extended tag in the Type column isn't enough) see that Start for /dev/sda2 is smaller that Start for /dev/sda5. And End for /dev/sda2 is the same that End for /dev/sda6.