type p - to list all your partitions type n - to create a new partition type l - for "logical" type t - to change the partition type to "Linux LVM" type 8e - for the "Linux LVM" type type p - to list the new partition table type w - to write changes and exit
sudo pvcreate /dev/sda3
sudo apt-get install lvm2
sudo vgextend 280g /dev/sda3