To add a single quote to a string, you include two ' marks e.g.
str := '''test string''';
Writeln(str)
In the string above, you have the normal single quotation to start a string and then two for the single quote. Same goes for the end of the string.
You can also use # followed by a number for other escape character e.g.
For a new line:
str := 'Newline' + #13 + #10
or just
str := 'Newline'#13#10
Of course, using the platform-dependent constant for newline is better.