I am a programmer. Given a sprite sheet, I can code game as per the requirements. But I do not know how to create these sprites. I use Cocos2D. And I do not know where to begin. I have never done anything art-related before. I am aware of TexturePacker. But it only packs already created sprites. So how do I get started with creating 2D sprites? Are there any dedicated softwares for this purpose? Main main concern is about creating assets for Retina Displays.
Pixel art is a complex field. Many people start with tiles and then expand to animated sprites.
A good tutorial I can recommend is "So you want to be a Pixel Artist" by Tsugumo.
You don't need any special software. Any raster-based image manipulation program will do - for a beginner even MSPaint.