They say the universe is composed mostly of dark matter. I think they also say that dark matters holds everthing together. Can we believe this?

I do not have a clue what dark energy is.

Cosmologists put the amount of ordinary (i.e., the kind we're used to) matter at 4% of the universe. That's pretty weird.

The dark matter is matter we can't "see" but has a gravitational effect. That's not completely unbelievable.

But as for dark energy (73%), no one seems to have a clue what that is and they openly admit it. I think it's just a name for an effect that no one can explain. Maybe if astronomers had named it, they'd call it something prosaically descriptive like "the push factor". And particle physicists would name it something whimsical like "pistaccio ice cream".