What is the meaning of statement, all human beings are equal?

It means legally and morally no person by nature is entitled to anything more or less than another person.

So any reason why one person is treated different from another must be artificial and human-made.

Of those suicidal reasons there are many, so each person is generally treated differently than others.

The egalitarian principle affirms the opposite of previous beliefs that some people are entitled by nature to more than others. E.g. kings and nobility being appointed by gods to rule others, or white people being entitled to being preferred to non-whites, or men being more valuable than women.

This affirmation is not strongly consistent, as an example a typical morality is "women and children first" in emergencies, which is not commonly justified morally and not viable in law. Also laws of inheritance would still grant ownership of valuables based on biological descent in the absence of a will, which can be seen as a violation of the principle of equality. Another huge problem is abortion and the question if when this principle starts to apply.

But the existence of social difference in itself does not violate the principle, it does not require each human on this planet to own exactly on car, exactly one room in exactly one house and exactly the same salary and the same food every day.

You could read up on the different forms of egalitarianism, maybe start on Wikipedia (https://en.m.wikipedia.org/wiki/Egalitarianism):

Some specifically focused egalitarian concerns include communism, legal egalitarianism, luck egalitarianism, political egalitarianism, gender egalitarianism, racial equality, equality of outcome and Christian egalitarianism.

In terms of law, I would say it means all people should expect the same consequences for acting the same way, if the circumstances are equal.

For example:

Somebody who kills somebody, should generally get the same penalty than every other person killing somebody.

But killing somebody in self-defence is surely not the same like killing somebody without a reason.

Now you can say: Somebody killing somebody in self-defence should expect the same consequences than every other person killing somebody in self-defence.

So you can find any number of graduations of circumstances. If all circumstances of two cases would be the same, both suspects should get the same penalty, no matter who they are.