If you can't make the explosions and you want good explosions, then get them from the Alamdv2 Library. ( this link goes streight to the explosions http://fxhome.com/alamdv2/plugins/category/40/explosions
Then download one of the image streams.
Try this one. http://fxhome.com/alamdv2/plugins/view/1152/ground-explosion-10
I like this one the best.
When you have downloaded one go onto the media browser and click on the icon next to the blue folder and click on import image stream. Find the image stream you have just downloaded then click on Images then |1 then vc1 and click open then drag the explosion from the media browser to the timeline and you should have a prity good explosions.
Note: if the explosion you downloaded was a zip folder you should extract the folders in it.
I hope that this was usefull to you.