Meditation is simply the act of relaxing and trying to clear ones mind of thoughts. The idea is that by not focusing on any one particular thing you are essentially giving your mind a rest, thus reducing stress and hopefully improving health.
One of the easiest and most basic ways to meditate is to lie down on your back, place your hand on your stomach and then breath in and out deeply & slowly. When you inhale you will want to extend your stomach outward. When you exhale you will want to retract your stomach inward. While doing this, your goal is to focus only on your breathing. This can be harder than one expects & the goal is to be awake, but not thinking on anything in particular or letting your mind wander off on a million different tangents. Just focus on your breathing.
Most meditation gurus espouses the principle of “living in the moment”. To focus only on the current moment you are living in and to try and appreciate it fully for what it is. Good or bad. I am not sure how much I personally buy into this ideal, as there may be times when you are having a terrible time & it’s very hard to find anything positive coming out of it. However, almost anything is worth trying at least once or twice. You may find that meditation helps you in your journey with IBS.
For a very thorough guide you might want to check out the book Wherever You Go, There You Are: Mindfulness Meditation in Everyday Life.