Positioning components on the screen is a little tricky in the beginning because as you may know, there’s hundreds of different screen sizes.
So one way to make your app look good in any type of screen is to have a relative positioning system instead of absolute.
You want to place them in an absolute way, exactly where you want them and that is not a good idea unless you are going to use your app in only one type of device.
To place the components in the screen use arrangements, which are containers. You have to set the screen to align objects to the left, center or right. Then the arrangements will have their own alignment too. Also give them the right size (automatic, percentage, fill parent or pixels).
By combining these settings, you can position your components in a way that will look correct in almost any screen size.
See this for a better idea of how it works: