I know it looks very old, that's because i've had it for 4 years now, he's a senior or something like that. It's all washed out as you can see, and the thread from the edges is starting to get loose... maybe i'll have to sew it again.. sometime. 
You can stuff it with old pieces of fabric, cottons, etc. For this i used at first some cottons but then i noticed that they kinda turned into a big big cotton ball and i didn't like the look of it so i trade them for pieces of fabric. To be more specific i used the stuff that you can find inside an old pillow. You can sew it using colorful thread [recommended] . I also recommend you to sew it from the outside not the inside, this way you'll have all the stitches visible and that's what it makes it look cool i guess.. You can use as many buttons you want, you can make him/ her/it happy-sad-neutral , i don't know. I made a happy one. [yes, that pink thread it's a smile]
Things you'll need:
*Fabric [any color]
*Buttons
*Needle and thread
*Something to stuff it [ cottons< not recommended, old fabric pieces, etc]
*Scissors
*Time and dedication :)