If you have any questions or requests for tutorials, post a comment or pm me.
MS Paint will work just as good as IrfanView, but I like IrfanView better and suggest you try it. I save my images as png because it supports transparency in the images, and it can look sharper then a jpg or gif image file. gif also supports transparency, while jpeg does not, but jpeg usually is the smallest file size.
You can also resize/crop your images with Paint or IrfanView before you upload.