not all vaccines. some vaccines (most olden ones) were just differnt similar or weaker or less potent strains, which while still infected you, you get some immunity because your body made “ammunition” against the actual threat.

then there are vaccines like mrna vaccines, where we find the mrna sequence that enocdes for specific protiens, for example, some surface protien. this protien is a part of virus, but alone the protien is pretty much useless. your body still sees that their is a foreign protein, and builds ammunition against this protien. when the actual protien with the specific virus comes, our body sees the same virus, and uses the same ammunition.