If you're able to select the bookmark from the list, then it seems bookmarks are being made successfully. (When I said no spaces, I meant no spaces inside the name... CustName, not Cust Name.)

Go to the Review tab and make the Track Changes button doesn't appear to be turned on.

That is what you are making by using the tools to insert fields. To see the fields that you are inserting, hold down ALT and press F9. (ALT+F9 again to turn the display of field codes back off.)

They should look something like this:
{ ASK custname "what is the name" \* MERGEFORMAT}
{ REF custname}

YOu can insert the fields manually...Hold down Ctrl and press F9. This will make the brackets. Then type the text in the brackets. You can see the syntax in the example above.
You cannot type the brackets. They must be created using Ctrl+F9