I just bought a new laptop (Lenovo) and I was reading the instructions when I came to the warning section?

The radiation it means is the laser to read the disk and the EM radiation released by the Wi-Fi antenna, and general radiation caused by electrons moving through wires. THESE ARE HARMLESS, they simply aren't ionising enough to cause any damage, however if you were to look into the laser of the disk reader (Which would be incredibly hard to do without taking the laptop apart when powered may I add) then you may be temporarily blinded depending upon which laser your laptop is using.

The battery thing is a issue with most laptops, what happens if you charge your laptop and keep it at 100% is that you start to reduce the batteries health, (the amount of charge it can store) So to reduce this damage you should let it discharge to a low level and then charge it back up to a figure lower than 100%

However 99% of people I know don't do this and, yes their laptops batteries have suffered but not to the point where its useless, it may have lost half an hours worth of battery life on each charge.

All electronics give off radiation. But the amount given off by a laptop (and the DVD drive when open) is so small that it will not harm you unless you were to expose yourself to it for hundreds of hours non-stop. You will get more radiation just by holding your cell phone close to your head while talking on it. (And you will probably do that for thousands of more times then you would ever expose yourself to the laser in your DVD. How much of the time do you have the drive open? Almost never.

As for the battery, you can do it either way. Complete drain or low drain. Does not matter. Switch between. Usually the problem is NOT how much you drain on the battery, but how much you overcharge it. Too many people have a habit of keeping their laptop plugged in all the time, which means that the battery continues to be charged even after it is 100% charged. Over time, that will decrease the life of a battery. Rather they should run the computer on the battery the majority of the time, and only plug it in when the battery needs charging. Once it is charged (or mostly charge) unplug it and run on battery until it needs charging again.

You should separate out your three or four questions. I'm only going to answer one of them.

This radiation thing is just Health & Safety panicky nonsense. The laser light can only reach your eyes if the laser is on when the DVD drawer is open. This can't happen in normal operation - when the drawer is opened, the laser shuts off. To have the laser operating while the drawer is open, you would have to smash the laptop open. You aren't going to smash your brand-new laptop open, are you? Well duuu-uh.
The Health and Safety law that forces those notices to be there's an idiotic law, made by idiots for idiots.

No, you should charge it to 100 % and then remove power until the battery low warning comes on. Then plug in power till it gets to 100 % again. The ony dangerous radiation is the laser beam of the CD drive as looking directly into ANY laser could cause permanent damage to your eyes. You could equally damage them looking straight at the sun. But the laser os OFF when the tray is open or is hidden inside the case depending on the type of drive. Other radiation would be from the wireless network adapter, but its' power is regulated by law for health reasons anyway. Less power than a cell phone.