what is mean by "COMPILING LINUX KERNEL" ? and
"INSTALLING A KERNEL PATCH"

it means compiling the central kernel image from source code. If you don't know what it means, you don't need to do it. It's a moderately advanced thing to need to do, so very unlikely to be relevant to you if you need to ask this question.

Sure it's not the right time for OP to try it, but it might be a good time to start reading about it.
The Linux kernel is the piece of software that makes this damn thing work. It allows software to communicate with the hardware and with other software. There is a procedure to compile your custom kernel. In short, download a kernel tree, configure it appropriately for your computer(s), compile and install it. If you google "how to compile linux kernel" will give you more than enough for reading.
I hope I clarified this a little bit for you.

You compile the kernel to configure/customise/tailor kernel drivers (modules). I wouldn't dismiss learning about it, even in the very early stages of using Linux, as the understanding of the kernel build process enhances the ability to troubleshoot the system and its hardware. You may think you don't need to do it, but once you've learned what it's about you may find you want/need/should do it. Word of warning. Never perform experimental rebuild on a live system and never do on the system that is subject of some maintenance contract without it being OK'ed by your provider - or you may invalidate the contract. Re-compiling the kernel to install a patch may be even more important, as patches are often essential security or bug fixes. Start reding at www.kernel.org/faq.

Compiling the Linux kernel means converting the source which is written in C ,a programming language, to machine code.
That are ones and zero's with which a computer can do calculations etc. The kernel has many different options. And sometimes people need a option which is not compiled in their current kernel. So they activate the option in the source and then compile it and replace their current kernel with the new compiled kernel.
A kernel patch is a adaptation to the kernel source for a new option or to repair a bug (error).

Above is all good answers. Here may be the most simplistic answer.

The kernel is basically the file that is the OS. Like any file it is made up of parts. Almost everything that the OS does has some part used in the kernel. For example the ability to use a processor is a part. When you take all the parts and settings for your system you can use a build feature to puts all the parts together. That is what is called compiling. It is the building of parts to a single file. When the OS works it may go to each part for instruction as to how to use a piece of hardware, like the cpu for example.

So a kernel patch is some code or file that goes into the kernel to fix or edit one or more of the original parts.