simplest possible teaching on the four Satipatthana
One of the simplest renderings of the 4 Foundations of Mindfulness is:


  
And what, bhikshus, is right mindfulness?
Here, bhikshus, 
a monk dwells  exertive, clearly knowing, mindful, observing the body in the body, 
   removing covetousness and displeasure in the world;
a monk dwells exertive, clearly knowing, mindful, observing feelings in the feelings, 
   removing covetousness and displeasure in the world;
a monk dwells exertive, clearly knowing, mindful, observing the mind in the mind, 
   removing covetousness and displeasure in the world; 
a monk dwells exertive, clearly knowing, mindful, observing dharmas in the dharmas, 
   removing covetousness and displeasure in the world.
This, bhikshus, is called right mindfulness.

  


(Magga) Vibhaṅga Sutta similar passage in Sacca Vibhanga Sutta

"removing covetousness and displeasure in the world" means you are to be equanimous without getting attached to the pleasant or averse to the unpleasant. You have to see impermanence also to remove ignorance.