I was able to cobble together the following instruction list for installing Xubuntu. I did the install but somehow it created grub2 which now with or without my Xubuntu flash drive installed grub2 appears and requires selecting Windows 10 (not a big pain as it is seldom used).
Is there a simple way to remove the grub2 (guess it is on the hard drive) without reinstalling Windows 10?
I would like to have Xubuntu work like my Fedora where it boots my flash drive according to boot order.
Thanks 4 the help. Here is what I did to install Xubuntu 16.04.1 from the CD/DVD:
1) Insert the Ubuntu Live CD/DVD, switch on the computer
with the boot order of 1) CD/DVDs, 2) USB, and
3) HDD.

2) Insert the USB Flash Drive to which Xubuntu will
be installed.

3) It will take a couple of minutes to load and you will
be presented with two choices:
'Try Xubuntu' and 'Install Xubuntu'.
Select: 'Install Xubuntu'

4) Here English is pre-selected so:
Click: Continue

5) Here the user is offered use of WIFI to download
updates etc.
Select: the non-WIFI approach to speed the install.

6) A "Prepare to Install" dialog box appears.
Click: Install 3rd party software.

7) An "Install Type" dialog is presented.
Click: "Something Else"
at the bottom of options.

8) With the USB flash drive inserted a list of hard
and USB drives, the Partitioning Menu is displayed.
The Primary hard drive is shown as 'Sda' followed
by any partitions that are on it like Sda1 or Sda2.
Below this is the USB drive, listed as 'Sdb'.
Click: /dev/Sdb1
the only partition on the drive Sdb.

Create a swap space 2 times of physical memory for
a swap space. If memory exceeds 8GB then something
like 2GB will be OK.
NOTE: the type is swap.

Select 'change' at lower left of Partition menu.
Enter: Size: (2000 MB)
Location: At beginning of parition
Use as: Swap
Click: OK

Now below the swap partiton in the menu, create a
root (/) partition with ext4 formating.

Click: "free space" which will appear below the
swap area in the main menu.
Select 'change' at lower left of Partition menu.
Enter: Size: (29743 MB, if flash drive is 32GB)
Location: Logical
Use as: Ext4 journaling
Under Mount Points:
Enter: /

If preferring a separate partition for a home
directory create it now like as above.
The single / (root) partition is sufficient.
NOTE: the type is ext4.

When installing on a UEFI PC, Sdb1 is swap and the
next partition shown is / and the partition is Sdb5.
The partitions 2-4 are for UEFI.

This returns to the previous menu and that partition
must have a check mark next to it.

9) Click on 'Sdb' just above /dev/Sdb1.
This SELECTS it as the device to INSTALL TO.

After satisfying the above:
10) Just below is an option for where the bootloader is to
be installed.
** It is VERY IMPORTANT that you CHANGE THIS OPTION.
** THE BOOTLOADER MUST BE INSTALLED TO YOUR DEVICE
listed as '/dev/Sdb'.
WARNING: If you do not do this the bootloader will be
installed to the INTERNAL HARD DRIVE.

11) Now it is ready to install to the USB flash drive.
Click 'Install'.

Answer a few simple questions like:
'name' and 'create password', then sit back and relax.

Plug in the new Xubuntu flash drive to use it on
booting.
The HD system will load if the flash drive is not connected.
The USB installation may take 3 or 4 minutes to fully boot,
especially if using a low quality USB flash drive.

If anyone finds an error or better step explanation please tell me.

I'm confused. Did you install the Xubuntu to the flash drive and is there anything installed to the computer hard drive in addition to Windows? That would explain this:

Did you install Grub to the MBR or to a partition?

No there is no error. If you installed the bootloader (Grub) to /dev/sdb as you said, and set the boot order cdrom, USB, HDD, then you will get the USB's boot menu when you boot. If you want to boot straight into Windows with no Grub menu, remove the USB flash drive.
You did say that "The HD system will load if the flash drive is not connected." - so it is all good.

@frankbell: me confuzed 2!!! I clicked nothing other than what is in the list.!
I wanted grub2 on the device so clicked /dev/Sdb see instructions.
When I pull out the flash drives I get grub2 prompt on booting. To that I "exit" and can get to W10 after clicking on HDD in (I guess it is grubs boot order which is cd/dvd, USB, and HDD) same as what I have in the systems boot order.
If I install my Fedora flash drive it boots to the flash drive.
If I install Xubuntu flash drive it eveeeeeeeentually gets there after clicking on "ubuntu".
BTW can also get to W10 if I click on "Windows boot manager" as I recall (that goes ubuntu, Windows boot manager, Ubuntu).
Wanted to be able to boot as I do with Fedora i.e. if it is installed. Pretty darn sure I did not inadvertently click anything for Sda as I knew that would screw stuff up like this.

I think grub2 is installed on the MBR as evidenced by the above. I am trying to determine whether to try resetting the MBR via DOS command from W10 or dd via Fedora.

@TxLonghorn: the flash drive target was plugged in from step 2 onward.

Please post the result of the Boot Info Script.
Boot your xubuntu and install boot-info-script:
Then run the script:
It will create a text file. Paste the contents of that file at pastebin.ubuntu.com - and copy the resulting link to the forum.