The efficacy of the vaccine indicates how well the vaccine has taught the body to make antibodies for the virus.
Thus, those vaccinated have a better chance of fighting the infection. That is why there are higher survival rates among those infected but vaccinated.
Since even vaccinated people can be infected, and since infection has a higher spread via inhalation and exhalation, wearing a mask keeps the virus out to a high extent, and helps keep the virus in as well (preventing the virus from spreading around via the infected person's exhalation).
Asymptomatic infection, and presymptomatic infection, are both forms of infection. However, yes, they differ from symptomatic infection in terms of severity, no doubt due to lesser viral load.
The distinction I would personally make is exposed vs infected. Being exposed to a virus doesn't mean you'll get infected, where infection is quantifiable tested with a PCR test.
For people that have received the vaccine in the last 6 months ("within date") the per-capita infection rate is an order of magnitude lower (per capita of ~1-4 vs ~15-30) than both the expired vaccinated and unvaccinated.
But when you look at ICU cases, the expired vaccinations are closer to the within-date vaccinations.
So keeping up to date on vaccine means you don't get infected at all. But having even an expired vaccine means you'll have a milder case.