Hi Dave,
Assuming these are all 12 volt panels you will want to connect 4 panels in series. That means connect the +ve of one panel to the -ve of the next when you are all finished connecting these 4 panels you should have one -ve lead open from the first panel and a +ve lead open from the last panel. This will make a 48 volt array.
With 20 panels you can make 5 arrays (4 panels per array)
Now if you want to use all the panels for charging or other purpose you can use each array alone or you can parallel them. To parallel two or more arrays you connect the +ve leads of each array together and the -ve leads together, these will now supply your output.
Hope this helps and have fun,
Hank