First you have to scan the picture. I'll assume the scanner came with a manual of some sort that will tell you how to do that. You might want to then edit the picture, resize it and such, but that's a whole nothing story. Then you need to put the picture someplace on the internet so people can see it. I use geocities, but there are all sorts of hosts out there and most isp's (the company you connect to the internet through) give you some space as well. Once that's done you put a link to the picture in your blog and everyone ooohs and ahhhs over it.
So as an example: stick picture in scanner, hit magic scan button. Copy resulting picture.jpg to http://test.url.com/picture.jpg, then make article with picture code of <IMG SRC=http://test.url.com/picture.jpg>. Your filename and url will most likely be different, but that's the general idea.
Hope this helps, if not, well ask again on whatever part is confusifying you.