first you will have to share the folder (Machine -> Settings -> Shared Folders -> Click on the green Plus on the right side)

# create mount point
mkdir /media/host;
# mounts the shared folder DATA
mount -t vboxsf name_of_share /media/host;

# if you want allow non-root users to mount host's share
# mount for access for non-root users
# find out what uid/gid user has
cat /etc/passwd|grep username;
chown -R 1004:1004 /media/host
mount -t vboxsf -o uid=1004,gid=1004 vms /media/host
admin