Translation:These things are impossible to understand.
Why ' à ' comprendre? Isnt ' comprendre' the infinative... meaning 'to understand'
Certain verbs are accompanied by specific prepositions before the infinitive.
Unfortunately they doesn't correspond to English prepositions and there isn't any particular logic to it. The good news is that the more you write and practice with these verbs, the more natural it will be and the less you will have to think about it.