Answer:
Half the hand, then ball your hand into a fist, make sure you don't have any rings or watches on.
Use lube, like crisco or lotion. Then massage the anus. Make sure to go to the bathroom and clean out your hole before doing so. Then stick a finger in one by one, when you reach two fingers, try to spread them apart inside to stretch your hole. Increase by fingers and do the same. Don't try to do this too fast. If it hurts, go back to what you were originally at and continue with that. If you are beginning it will take a while. When you can reach all 4 fingers, try it all with your thumb. To do this, make a duck form with your fist. Sorta like your making a shadow puppet. Then slowly enter. Take a deep breath. Exhale. And go deeper, you can feel the path of the colon this way. It curves inwards. Try to slowly spread it as you go deeper. Don't rush, it will hurt if you do. Make sure that you are very well lubed. Once when you get deep enough, get the rough part over with. which is the muscle near your thumb. Try to easily force it in. The more lube there is, the easier it is. Once when it is in, it will hurt. Simply take it out slowly by exhaling and sliding it out. It may hurt. If it hurts too much, go back to just 5 fingers and go in and out fast and slow, spreading your fingers each time. Going fast will also help loosen the muscles.