I'm installing Ubuntu 20.04 using Dave's RoboShak instructions for dual boot installation. Earlier I partitioned 30 Gb in Windows to use for Ubuntu.. now I'm at a stage in the instructions that doesn't line up with what I'm seeing... for Installation Type the screen shows various devices like /dev/sda1-4 ntfs , /dev/sdb1-4, and free space. I'm not sure what to do here... any advice is appreciated

The first question that comes me is, when you freed up that 30GB for Ubuntu, did you also format the partition?

Beyond that, it would help if you would provide more detail about the current partitioning. The command fdisk -l will provide that information under Linux (it's been so long since I touched Windows I can't remember the Windows equivalent.)

If you created a partition in the empty space left by shrinking windows, delete the newly created partition, reboot the ubuntu installation. You should then have an option to install along side windows.

It is usually recommended in your situation to use Disk Management in windows to shrink the largest partition on windows to create free space, then reboot your windows to verify no problems. It is unlikely that you would be able to format a partition for Linux from windows with default software and that would be necessary. Often recommended to run chkdsk also from windows on reboot. Using free space as suggested above would be the way to go.

If the free space you see is on the drive you want to use for Ubuntu, install there. Also, you might have posted a link to the site you used for instructions.