Trump's "Operation Warp Speed" Vaccine Plan--"A Few Hundred Million Doses"

I believe it is an RNA vaccine. From the wiki on them:

Just like normal vaccines, RNA vaccines are intended to induce the production of antibodies which will bind to potential pathogens. The RNA sequence codes for antigens, proteins that are identical or resembling those of the pathogen. Upon the delivery of the vaccine into the body, this sequence is translated by the host cells to produce the encoded antigens, which then stimulate the body’s adaptive immune system to produce antibodies against the pathogen.

In plainer English, you snip the RNA sequence responsible for telling cells to build those spiky and other proteins on the surface of the virus. The body's cells scan the free RNA and then build the proteins. The immune system immediately gets they are foreign and builds antibodies against them. Antibodies and a kind of cellular institutional memory that will stave off an infection.