Yeah, can't show you a diagram, even if i could, am artistically inclined for that.
Well, it is like normal vaginal sex, except you are entering the bum hole, the most common position for it, is the one receiving gets on his/her knees, and the one giving anal is behind.
And it is important to use lots of lubrication, especially if you decide to use a condom, as anal can be a bit painful for the one receiving, it is good to stretch gradually, perhaps starting out with a finger, then two fingers, or even purchasing different sizes of butt plugs at a sex shop. If the receiver is not good with gradual pain, you could stretch it all at once, and be done with it, but be careful as you can cause tears if it's not properly lubricated.
As soon as the stretching process is done, they will be able to enjoy it fully.
Despite myth, anal is actually very clean, however, unprotected anal sex can lead to harmful std's like HIV more than vaginal sex, so it is probably good to get checked for those things with your partner or make sure you can trust they are free of diseases.
There's no way to visually illustrate that, here.
You would approach anal much the way you would approach vaginal... albeit, somewhat differently than oral. Use care and precautions as this is an unsanitary practice that could
lead to bacterial infections.