I can not Customize in normal way.

HI, I bought it but, I don’t know where should I give the purchase key because I saw WPbakery builder needs a key, I have brought a premium key, Why I can not use it?? and I cant customize it in the normal way, I don’t understand which demo I should install? I installed the demo but now the website looks so odd. very bad. please if you have give me a tutorial link or help me to install the demo properly.