So, I'll use an analogy, think of the virus as a bomb inside a lockbox that can only be opened by a specific key. If you can open the lockbox, you can disable the bomb and all is good, but as time goes on, the bombs duplicate so the longer it goes, the more bombs you need to disable. The immune system can be seen as the bomb squad who is responsible for defeating the bomb. The bomb squad has a collection of keys for different bombs and will try them, but if they don't work, they have to work on developing a specific key.
This is where vaccines come into play:
Traditional: You give the bomb squad a disabled bomb, or weakened one (so instead of an explosion, it just gives a puff of smoke), and they work on producing the key. Obvious side-effect if they don't do it in time, the bomb could reproduce and explode, but the damage is significantly reduced.
Virus analog: You give the bomb squad something that looks like the bomb, and has a similar lock. You won't get an explosion if things go wrong. The drawback is that the key developed by the bomb squad may not fit the real thing; however, it will speed up the process of making the key, so bombs may go off, but not as many as if they didn't have the analog.
mRNA: You give the bomb squad the specifications of the lock, and they build it. They then develop the key to open the lock. So, no chance of explosion, and the key will definitely fit the lock of the real thing. The problem is that the specifications are printed on tissue paper and if not handled correctly, they may not see the plans to build the lock, so they never develop the key.
Of course, variations and mutations can occur which may modify the lock so that the key doesn't fit 100% securely; however, maybe enough to open a few locks, or the keys need slight modification. It may mean a few explosions, but you wouldn't suffer the full effect.
Those are generally the different types of vaccines. There are nuances, but as an overview, I think that would be understandable.