Don’t do yourself down - there’s so much information out there, and some of it is very unreliable.
The vaccines work by introducing a protein into the body that looks like it’s part of the virus. This alarms the immune system to produce antibodies to fight the intruder. As the protein is harmless and can’t do anything, the body quickly thinks “job done - intruders repelled. Better hang on to the details of this one in case we see it again” and gets back to normal. This fighting mode sometimes makes the recipient feel a bit ill for a day or so, but there is no real infection.
All this takes 2-3 weeks to happen, and a second dose may be needed to make the response as good as it can possibly be.
Then, if the body is exposed to the actual virus, it’s already primed. Rather than being caught on the hop and having to develop antibodies in a real battle situation, the antibodies are already there or can be made very quickly to mount a good defence.
In some situations this is enough to completely overpower the virus and you don’t get infected at all. In other situations the antibodies don’t completely overpower the virus but they do a pretty good job of suppressing it. You might feel fine and not know you’re infected at all, or you may have Covid, but more mildly than you would have had if you had not been vaccinated. Unfortunately some people won’t respond at all to the vaccination (it’s unpredictable) so they are still as at risk as they would have been.
Interestingly, the Astra Zeneca (Oxford) trial showed that all the people who had a vaccine and then still developed Covid did not become critically ill, which is great news.
As yet, we don’t know what proportion of recipients will be completely protected from infection, and what proportion will be infected but absolutely fine with no symptoms.
This means social distancing will be needed for some while, until either infection rates are really low, or until all adults have been vaccinated, or we can be confident that those people who have Covid but so mildly they don’t know don’t actually spread it very much.
Hope that makes some sense OP. I’m sure there must be some videos that explain this much better than I have.
I had my first vaccination on Saturday. I’m delighted.