I know there is a method to test your product idea using a landing page that describes your product, and asks for the user to enter his email if he would like to register for the beta. Then there is the thing that you provide links and then you analyze who from total users did what.
What I'm missing is step by step examples. How should I do this? What should this landing page contain? How should it look?
Has someone here actually used this method and can share their experience?
You are asking a simple question with a very complex answer. There are three steps to accomplishing your goal, each of which requires a great deal of background and detail in order to be done effectively:
Providing step-by-step details for all of these would take an awful lot of space, but that is the framework for accomplishing your task.
Others are very good answers, but if you want step by step instructions, Start Small Stay Small has a chapter on the subject.
EDIT: summary of approach - The Mini Sales Site *Works best for downloadable or web-based (SaaS) app.
JonDiPietro's answer is correct and the steps can be complicated to do 'right' but if you just need to get going and get started here are some ideas.
a) Consult a local web developer... OR
b) Follow these steps:
You can Google or probably YouTube tutorials and educational articles on any one of these individual items. This will get you started at least.