Actually, it is quite easy to do. Virtually all retail boxed HD's come with disk imaging software and good instructions, either in the box or on the manufacturer's website. In addition, there are good freeware applications available if an OEM drive is purchased (Macrium Reflect is one). As far as Windows not liking it, while it is true that you can't just copy the os to another drive which would not copy the master boot record or put location specific files in their proper place, imaging(cloning) the drive is transparent to the operating system and windows won't squawk at all.Like others have said, copying a whole drive including operating system to another drive is not easy to do especially if you only have one computer. Windows does not like being moved and it is easy to not copy all the files.
With that said, based on the kinds of questions the OP has asked, I would also suggest that he/she have this done by someone who is more capable. "Learning" on a system with valuable data that hasn't been backed up is not a prudent course of action.
OP if you decide to tackle this on your own and need any assistance, send me pm.