How to prevent the blurring of images(png/jpeg) in adobe illustrator?

I am new to Adobe illustrator, and I read that in Illustrator works on some vector technique means you can change the size of image without getting blurry? I made my first logo and saved it as png format, but when I am increasing the size of image, its getting blurry?So how can i save my logo so when I increase its size, It doesn't get blurry? Thanks