How can I create a string containing a quote or a backslash?

Applescript FAQ Text Manipulation
#1

Quotes and backslashes are control characters in AppleScript. Therefore, you’ll need to escape these characters with preceeding backslashes when you write your code. For example…

set theString to "\"This is a sentence wraped in quotes.\""
--> "This is a sentence wraped in quotes."

set theString to "This is a sentence containing a backslash (\\)."
--> This is a sentence containing a backslash (\).