UCAS

What happens, if my predicted a level grade is lower then what I end up getting at the end?

Do the universities let me in?

And what happens after I put my application in, let’s say I’m below what they want, for my predicted. But I end up getting what they want in my real exam? What happens then??

Someone help me

The usual advice is to choose one or two 'aspirational' unis a grade or two above your predicted grades (you might/might not get offers for these), two/three at your grades and an insurance choice a grade or two below your predicted. By the time you need to choose your firm/insurance choices in May/June, you might have a better idea of how you are performing and can make your choices accordingly.
If on results day you have achieved higher grades than predicted and you don't want to stick with your firm choice, then you can see if any places are available in clearing for other unis. Alternatively, you can plan a gap year and apply with achieved grades in the following cycle.

There’s one university I really want to go too. The rest I fit the criteria for already. But, with the one I really want to go too. My predicted grade might be low due to circumstances such as being rushed. But my actual grade will definitely meet their expectations. So what happens? Do they automatically decline MeV

Unless your predicted grades are a long way off the entry requirements, apply to that uni first and see if you get an offer. You can then decide which other unis to apply to by the January deadline.