If you create a volume manually and then try to attach and mount it to an instance you will notice that the volume is not usable cause it is raw. Of course you will need to format it and then mount it.
It is very basic and simple task but not for beginners. So we will list the attached volumes, check the filesystem (which supposed to be nothing!), create file system, create mount point and mount.
lsblk sudo file -s /dev/xvdb sudo mkfs -t ext4 /dev/xvdb sudo mkdir mount_point sudo mount /dev/xvdb mount_point