What mrna vaccines do is give your own cells the instructions to build parts of viruses. In this case it tells your own cells to encode the sarscov2 spike protein. Now in a normal situation this would be a good thing. Your body would see the spike protein and learn to fight it off.
The problem is that the sarscov2 spike protein is actually poisonous. It damages any cells that it comes in contact with through signaling the ace2 receptor pathway. Getting covid is dangerous because it does permanent damage to your body due to its spike protein and the vaccine does the same thing. The vaccine flows all around your body, it collects in your lymph nodes, your bone marrow, and your ovaries (if you have any) and it does permanent damage to your body.
All of this is know, what is also known is that the original sars acted the same way. It also had a toxic spike protein. It is quite possible that this is all on purpose.