I have installed Visual Composer but there is no button appearing.
If you cannot see any button on your page editor then please make sure if you activated the Visual Composer.
1- It is not activated, simply activate it. It should work 2- It is activated, so simply deactivate the plugins you have and check if it is working then simply activate your plugins one by one.
For installation instructions of the Visual Composer http://www.screenr.com/30j8