TRK is in the first place known as a BOOTCD. So even if burning an isofile to a CD is about the simplest thing to do, I will nevertheless commit a piece on how you can get TRK on a cd properly.
If you really want a no brainer, try the executable, self burning version of TRK from the download section. You don't need any burn software to be installed on your computer, but it does require that you have administrator rights.
And how to do it: download, save locally and double click trinity-rescue-kit.3.4-build-366.exe (or the latest version), answer "Yes" after you made sure you have a blank CD-R in your CD writer and just sit back and relax.
If you want to burn TRK from the isofile, there are several options and programs.
For Windows 7 users it's easy: right click on the file and select the option to burn it to CD.
All other users have several possibilities.
1 free and rather easy possibility is to use MagicIso, which is free for isos up to 300mb. At the end of this document you will find it explained in screenshots.
Another free alternative is CD Burner XP Pro, which is a very good and full fledged CD burning software as a whole by the way.