I understand the language may be an issue. If there's anything particular that you found confusing, let me know.
The basic idea is that there are many, many different kinds of things called "preamps", so your initial question is impossible to answer. For an answer, you'd have to specify what kind of preamp, for what kind of application, you were talking about.
Another basic idea is that all electronic devices sound just a bit different, and sometimes you can generalize that you are familiar with the sound of certain features, which allows you to experiment with an idea of what to expect when buying a preamp. Otherwise it's all a random, subjective gamble, where the only way to understand is to try different ones yourself.