or you can learn how to do it without needing a bashguard and without using the teeth of your chainring (makes me shiver just thinking about it) to move yourself over it, but this generally is just a little more in depth of what was posted above
Start by knowing that there are log piles and pyramids that just can not be done cleanly without endoing. If there is a large hole in the backside your wheel will get stuck and stop foward momentum, or if the backside is too steep, you will just run your front end straight into the ground.
Assuming the logs dont pose either of these problems, it really is quite simple. It takes alot of practice and probably bent chainrings in the process, but if you focus on learing it right you wont have a problem.
First, make sure you keep your weight centered from left to right so that when you do hit the chainring, it will be less likely to bend badly. Most things on a bike can be done more smoothly with a little extra speed because the momentum is going to help you and this is not an exception. You dont need to be flying at the pile, but you need enough speed that you will get carried over it, it takes some time to figure that out, but generally, if you think your going to slow, faster is a little better if you are comfortable with it. if you are going to slowly, you'll know in a second anyway.
Just before you get to the pile you want to lift or "yank" (as we called it in BMX) your front wheel up with the intent on getting it over the top and placing it down just on the otherside of the top of the pile. This sometimes can't work because it is too high. generally try to match the angle of the logs with your bike and get your front whell over as soon as possible.
As soon as your front tire hits the backside you need to commit to doing two things, push your weight foward while tucking your back end underneath you. If you rode into it with enough speed, the middle of your bike will miss the pile in the process, it sort of just pops over.
Then practice makes the last part work smoothly, it is hard not to smack your back wheel on the top of the pile. you need to judge when the back tire has cleared the top, it usually is pretty quick. once the tire is clear, shift your weight to the rear end, so that you ride out and off the pile on your back wheel. the sooner you are on your back wheel the better.
It is a skill and takes practice, i am in no way the perfect and eat sh1t every so often, but it is more because you need to fully commit and every so often it just does not work, mostly because of on of the first two problems i proposed. there are other ways to do this, it is just how i do it.