I would like to add a Control + Left Arrow to switch my desktop to the left. When I use Keystrockes and press Control + Left Arrow, it performs the action and does not enter the command I want to assign to a button.

How do I fix this? 

Please follow the instructions I've included below, and this will get you set up. 

In this example, I will be setting up the 

You will need to open the Settings panel first.

[1] I have selected my Pen Tablet Small.

[2] Then, select the All Other icons in the application row.

[3] I'll assign this function to the top left button on my Tablet.

[4] I clicked on the Control button.

[5] Then, I select the Keystroke menu item.

[6] I will give the new Shortcut a name.

[7] Then, in the Keystroke Keys field, I press the Control key and hold it down.

If I press the Left Arrow now, it will activate the command, but I do not want that.

So I click back in the Shortcut Name field, and once I see my cursor flashing in the Shortcut Name field, I release the Control key.

I then move the cursor back to the Keystroke field and press the Left Arrow.

{7] The Keystroke field now has the Control+Right-Arrow in it.

Click OK, and you are set.

If you would also like to set the Right Tablet control Button to activate the Right Desktop, you can do that in the same way by using the Control + Right Arrow.