No idea how to do it??
There is plenty of free resources that you can learn C++ online and the bitcoin source is completely open. I recommend you just dive in and start.

The first step is taking the first step.

Agreed. If you just want to clone a coin, then-->
GIYF.
If you actually want to make something worthwhile (not saying that some clones aren't) then grab a source of your choice, go tot he SRC folder (if it's C++ based) and piece by piece deconstruct it using google to learn what everything does, and how to format in C++. After a while you will start to form a basic, and then, intermediate understanding of C++ and what makes these coins 'tick'. You will find yourself jotting down ideas, and things that you would like to do, and slowly find yourself writing new, if not, totally overhauled code for your ideas, starting at from a basic template.
Please, if you are going to make something, take your time and do it right. In the long run you will feel good about your work of art, and you would have started your venture into the world of wonders. I could have released a million different clones, but I chose not to as it looks terrible when a person is pumping out useless cash grabs. Instead I choose to slowly work on my own ideas, with no rushing, or set time limit. In the end, when (if ever) i release it, I will have a better chance of success, and long term sustainability.
So, TLDR, take your time, learn what it is you're doing, and enjoy the learning process!

MrC