How do I create my own textures for walls?

Please forgive my noobiness, but im trying to create a texture for a wall, such as bricks, wood planks etc… i want to make the texture myself (as my goal is to make a game where i created everything) is there a tool for painting or do i need another program? i know how to change the color of objects, but what i want is to turn my plain white walls into brick walls. (not sure if this is called a texture or not)

PS i have unity 4 free

I use a camera and Paint Shop Pro, but you should also get Bitmap2Material, it will save you a lot of time.

Use any image editing tool such as Adobe Photoshop.