how much 600px in cm

That means the picture your taking will have 600x600 pixels.

Here's a picture: http://upload.wikimedia.org/wikipedia/commons/thumb/2/2e/Pi-symbol.svg/600px-Pi-symbol.svg.png

It depends on your file system. Some filesystems are CASE sensitive but typically JPG and jpg are the same thing.

* matches anything. *.jpg would mean any file with a .jpg extension. 1*.jpg would mean any file where the name begins with 1 and ends with a .jpg ? matches any single character. ?.jpg would match a.jpg, 1.jpg, or F.jpg but not a1.jpg. Several ? wildcards can be used so that ??.jpg would match any jpg file with a two letter name.