Does your current code compile?
In particular, do these lines compile?
Also, you seem to be trying to add the same components to a JPanel and to the contentPane both at the same time. Why?
You shouldn't have a FlowLayout() statement when adding a component as you've done above, and also, it almost appears as if you are trying to call the FlowLayout constructor without new which is never done in
Java much less in Swing.
I strongly advise you to read the layout manager section of the Swing tutorials with attention to the FlowLayout, the BorderLayout, and the GridLayout. Later I'd add the BoxLayout, and much later the GridBagLayout. After reading this section, consider using nested JPanels to hold your components with each JPanel using its own layout manager. For instance you could let the contentPane use its default BorderLayout, then have a top panel that holds your jlabel, your jtextfield (though a jspinner that uses a spinnernumbermodel may work better here), and your jcheckbox. This could be placed in the contentPane BorderLayout.NORTH. Then add your jtextarea to a jscrollpane and add it BorderLayout.CENTER, and finally place whatever buttons you need, including the about button in its own JPanel that uses the default FlowLayout or GridLayout, and place it in the contentPane BorderLayout.SOUTH. Good luck, and YMMV.
Pete