The Open URL has a specify button that allows you to set up a calculation that produces the URL. If the correctly formatted URL is stored in the field, you should be able to just refer to that field by name in this calculation dialog. If it is not formatted correctly, you may need to use a calculation that combines the data in the field with the needed additional characters to produce a valid URL.
I follow you all the way up to "you should be able to just refer to that field by name in this calculation dialog."
If the field is named "Web Site" what would the calculation look like?
Web Site = ??; do I use a Get function?
In the specify calculation dialog that pops up when you want to specify this field, find the field's table from the drop down at the top, then double click the field's name in the list of fields that appears below the drop down to add it to your calculation.
Now when I try the same thing to capture an email address from a field it puts "Email Address" in the TO: line.
When I tried using the Send Email feature of the button, it gives me an error and shuts down my program. Any ideas on that one?
What do you mean by the "send mail feature of the button"?
Do you mean that you double click the button while in layout mode to bring up button setup..., then select Send Mail and click specify?
At no point in that process should FileMaker just quit. Such a crash suggests your file may be damaged (Either the damage caused the "crash" or the crash may have damaged your file.) Run a recover on your file and see what is reported by the recover process.
Things to keep in mind about Recover:
Recover does not detect all problems
Recover doesn't always fix all problems correctly
Best Practice is to never put a recovered copy back into regular use or development. Instead, replace the damaged file with an undamaged back up copy if this is at all possible. You may have to save a clone of the back up copy and import all data from your recovered copy to get a working copy with the most up to date information possible.