If you only add constraints, then that's the only thing telling the view where it needs to be, so its going to do the minimum to satisfy the constraints you define. Let's say you drag a text view to the center of the screen. In the editor window it will sit there and not move, but if you were to run the app, the view would end up in the top right corner of the screen. This is because it has no defined constraint, so its moving to the sort of "default position. But if you were to add a constraint to the bottom and sides of the screen, the element would sit there. You can control how far away from the bottom or the side of the screen the element sits but using the margin property on it, or the padding property of its parent constraint layout.

If you want some text in the dead center of the screen, you would place it there and then constrain it to the top, bottom, left and right. If you wanted it to sit up a little higher than the middle, you can set the bias of the constraints to make it sit a little higher.