When you place something somewhere, you put there. But if you misplace something, you put in the wrong place, and then you can't find it.
In other words, to misplace things is to lose them because you can't remember where you put them.
Sometimes I misplace my mug of tea or my cell phone, and I have to go searching for it. If you were just using your umbrella or your jacket and you misplace it, you might retrace your steps to find it, or you might sit and think carefully about the last place you saw it. Velma is always misplacing her glasses... which is not great, because she can't see well to search for them!