Verified answer

Downloading it for free is illegal, don't do it. GIMP is a good alternative, it's free and contains many features Photoshop has, too.

Photoshop is not free.

Adobe Photoshop can only be downloaded safely from http://www.adobe.com/ - there is a free trial you can use for 30 days, then you pay to continue using it.

Photoshop is raster image editor, it's not the only raster image editor. There are others, some are free.

GIMP http://www.gimp.org/ - the closest to Photoshop, legal and free

Paint.NET http://www.gepaint.net/ - simpler, but still good

Photoscape http://www.photoscape.org/ - simpler than Paint.NET but still good