A vaccine certainly isn't a cure, but it goes a long way to reducing the problems that this virus can cause. Like the flu vaccine, in simple terms a Covid vaccine essentially teaches your body what the virus is to allow you deal with it better should you become exposed to it. The aim is also to stop your body going into panic mode dealing with something unknown, which is why many suffered so badly when this thing first came about.
Now for some as with the flu vaccine, it might mean your body shakes it off without realising you've even had it, for others it might be a reduced severity of symptoms and for others it might not do a thing. In any case, like the flu vaccine, it goes a long way to reducing the number of patients who become ill enough to require hospital treatment. The more people who are capable of fighting off the virus quickly also means the fewer people who are likely to be exposed in the long run.
It's important not to think of a vaccine as one magic bullet to get us back to normality. However it is without a doubt the largest tool in a growing 'box of tricks' that's being used and researched as time goes on. Whether that's convalescent plasma, mask wearing, antibody cocktails or steroids. Even some studies on mask wearing are said to have helped the situation, as whilst they don't prevent exposure to the virus, they may have reduced the viral load received by those exposed meaning people have been more likely to have the virus asymptomatically.