While searcing about PHP speed I have read that opcode cache can speed up the PHP scripts. However, I do not know what is opcode cache and is it simple to implement in our scripts?
Could you tell me more about that? If I have many PHP files then will they converted to one file for example or each file converted alone so I can update specific page later on? And where should I install the You install the opcache? Is it free?
You should focus on learning PHP, learning about opcaches is not required at this time.
Nor should you have one while developing.
I've just seen that but want to know, is it difficult process?
You should not have to do anything with your scripts. You install the opcache and configure it that is it. Any scripts you wrote should work without any problems.