[sdabdoub]

The "central dogma"[1] of biology:

    DNA -> RNA -> Protein

DNA is read sequentially base-by-base (essentially like the read head on a HDD) by a protein called RNA polymerase. As it is reading, it produces RNA. If that RNA is meant to become a protein, it is post-processed to remove various bits and becomes a messenger RNA (mRNA). This mRNA is inserted into another huge protein called the Ribosome[2], and is read 3 bases at a time. Each set of 3 bases corresponds to a single Amino Acid. The string of amino acids produced by the ribosome is a protein.

So the mRNA in the vaccine simply contains the instructions to produce a copy of the spike protein from the COVID-19 virus. When your body produces enough copies of that protein, your immune system takes notice that a foreign protein is floating around and begins the process to recognize and memorize it for future use. (that last part is super simplified).

[1] https://en.wikipedia.org/wiki/Central_dogma_of_molecular_bio...

[2] https://biologydictionary.net/wp-content/uploads/2017/01/Rib...