It is hard to understand and try to explain. But this is it in a nutshell:
In a normal criminal trial, there would be a crime attached to every charge in the indictment. In the Trump trial, there is no crime. There are only multiple allegations by the prosecutor, some of which never were part of the trial testimony, but were only in the prosecutor's closing argument.
The judge boiled them down to three alleged crimes, none of which were actual charges in the indictment against Trump. Normally, jurors must make a unanimous decision on each charge, but the judge said these jurors do not need to unanimously agree on any of them to find the defendant guilty. They essentially can mix and match to come up with 12 guilty verdicts in aggregate. Not 12 for each separate charge, but any number for all the charges that add up to one combined 12.
Not only is this confusing as h3ll, but it is also severely unconstitutional.