Hi,
That is a very big request. Solar flares are explosions which occur in magnetic loops just above the Sun's surface. They release lots of light, especially kinds of high energy light we can't see, like X-rays, but also visible light and radio waves. We think they happen because the sun's magnetic field gets all tangled up and stressed. It snaps into a less stressed form and releases energy. This is the same explanation I give for coronal mass ejections (CMEs), which involve material shooting away from the sun. Flare and CMEs can be associated with each other, but not always.

There are some pictures of flares taken in ultraviolet light taken by the TRACE spacecraft:
http://trace.lmsal.com/POD/images/T195_020421_014352.gif
http://trace.lmsal.com/POD/images/T1600_001124_150901.gif
http://trace.lmsal.com/POD/images/T171_010419_1330.jpg

cheers,
Terry