ok i hear this all the time "compile the kernel, i compiled the kernel, i recompiled the kernel..."
what does it mean?? i mean i cant really imagine what the purpose really is, what for?
it would be nice if somebody explains it in a few sentences, and understandable for dummies like me.
thanks in advance.

The kernel is the actual operating system itself. Most distributions ship large kernels compiled with support for as much hardware as possible so that it works out of the box. If you recompile a kernel yourself you can leave out drivers that you don't need and select other options which, depending on your hardware will give you a performance boost.

thank you now i can imagime much more about that, so are there any manuals? i mean good manuals

There is a guide on the LQ wiki:
http://wiki.linuxquestions.org/wiki/Compiling_a_kernel

The actual options you choose for your kernel will vary between machines so there is no exact howto.

The Linux Kernel is basically the spine of your operating environment. It provides support for all your hardware and performs essential low level functions.

As mentioned before, operating systems such as Windows and Mac OS X come with a kernel that has already been compiled for you, which includes support for a wide range of hardware already. These kernels usually have very nice features compiled in as well, such as "Plug and Play", or hardware autodetection, built in. In these cases, you don't have to be concerned with the kernel and don't even have to know that it exists.

The Linux kernel, though, is open-source, meaning it can be customized to meet your own requirements. Why compile support for such a wide range of hardware when all you really need is support for the hardware in your machine? Why compile support for hundreds of network cards when really you only need support for yours? That's what compiling a custom kernel and recompiling the kernel is for.