The top graphs show the output from each of the individual receivers. You can normally see a large slow hump in these graphs as the Milky Way passes overhead. You may also see Jupiter activity, solar radio bursts, or ionospheric fadeouts caused by solar flares.
The bottom graph shows the interferometer output. Whenever a "compact" radio source moves across the sky it will produce a quasi-sinusoidal ("squiggly") line in this graph, called an interference fringe pattern.
For more information about understanding this data, and about Simple 20MHz
Interferometers, please visit these sites: