I have some free space (not partitioned) on my disk drive. I have not configured LVM during installation.Is it possible to modify some of the existing partitions to be a member of LVM?

go to google then find the howto lvm

If you mean non-destructively -- no, it isn't. You have to copy your data somewhere (external USB drive) and copy it back after setting up the LVM. If you also want your system partition to become part of a volume group, it is a little more complicated, because you have to make sure your system boots entirely from the external drive -- but it is possible, btdt

quite a reply!

Assuming you have two new hard disks each 250 GB /dev/sdb and /dev/sdc. Say you wanted to mount this LVM to your home folder.

Create Physical Volumes
Create a Volume Group
Create a Logical Volume
Note: you may have to play around with the -L option until you find the correct one. It may be 460 or 480. Make sure to maximize your size. You can always 'lvremove my_lvm_name' and try again.

Then label it

e2label /dev/lvm01/my_lvm_name /home.

Then add the entry to your /etc/fstab file. Instead of listing the device with the path /dev/lvm01/my_lvm_name, just use LABEL=/home.

Later on if your /home folder gets full you can buy another hard disk /dev/sdd and add it by doing
Enjoy!