Covid has a protein on the outside of the virus and uses this protein to enter our cells. That protein makes the virus more infectious.
The scientist studied the DNA sequence of the virus and found the sequence of DNA that is the blueprint for that protein.
The scientist took the DNA for the protein on Covid and made an mRNA (messenger RNA) version of it. That the vaccine.
The vaccine contains no actual part of the virus. It has the instructions on how to make the protein on Covid. So you can’t get infected with Covid from the vaccine.
The cells sees these instructions and make a bunch of the protein. The immune system sees this new protein the body is producing and immediately starts attacking the protein on the covid.
The fever,chills,muscle soreness etc one might get a vaccine side effect is body fighting the covid protein.