Vaccines work because our bodies produce antibodies whenever an illness starts to form. A vaccine introduces a dead or weakened virus to your body. Your body produces antibodies when introduced to this virus. This overwhelms any sickness before it can grow.
The viruses that are used for vaccines are either dead or so weak that they cannot be caught. Even children with a mild illness are usually fine to be vaccinated.
Each vaccination you give your child is designed to treat a very serious condition or conditions. They all are essential. While it might seem like a lot for your young child, their vaccination schedule is completely safe.
The frequency of side effects varies depending on the vaccine. You can find more information here. Vaccines are tested to make sure that they are safe and effective. The rare occurrence of side effects is outweighed by their benefit.
There is no legitimate evidence that any vaccines cause autism. The idea that vaccines could cause autism is a result of a flawed medical study. It came from a doctor who has been stripped of his medical license. Research has shown time and time again that vaccines do not cause autism. There is zero risk of it.