There are different kinds of silent retreats. In the Zen tradition, I am told, you should normally have been meditating for some time to be allowed to enter a silent retreat. You are given a cell and are delivered meals. You are by yourself and your practice is what you choose it to be. In the Vipassana tradition, as taught by Goenkaji, you enter a vow of silence but live and meditate in a community of other meditators according to a strict schedule and code with guidance and support. All meals are prepared for you. But you may not have any books or any diversions such as writing materials, music, and so on. You also need not have had any previous experience in meditation. Silence is essential for the teaching.
Is it dangerous? Is it boring? It is not recommended to do a silent retreat if you are suffering from deep emotional turmoil or substance addiction. It is better suited for people in a more calm moment of their life as it is a mental challenge. People with certain physical ailments should also consider whether they can endure the physical discomfort of long periods of immobility. However, because you can choose the position that is most comfortable for you for your meditation most people, even with physical ailments, should be able to meditate in time in a position that is comfortable to them. Initially you will probably find many moments of boredom, because you will not have many of the diversions you use to avoid observing life quietly. But this is a normal part of a silent retreat and is what helps you focus more clearly on what is going on in your mind and your body which is, in large part, what a silent retreat is about.