JAVA。 JFrame中的背景图片，drawString，JButton和JComboBox

I'm new at working with JFrames. So I dont really know how to draw/paint/display everything in a JFrame. Im working on a memory game. Currently im working at the first form, this form must display a background image, a welcome text, a dropdown list with the amount of cards for the memory game and a button which should start the game. I succesfully displayed the background image and the welcome text. After adding the JButton and combobox my form got messed up (I only see a blue background). I have no idea what im doing wrong, also I dont know how I can place the button and dropdown on the right x and y position. I want to place the dropdown box under the welcome text and the button to the right of the dropdownbox.I'm new at working with JFrames. So I dont real