I want some explains about this task, I cannot understand what should I do exactly

This is a simulation of queueing within a scheduler, but it's an incomplete description. How many queues are there supposed to be? How is the work time for an arriving process determined? Is an arriving process queued according to its priority or something else? The description has to include those things, but you've omitted them.

First, you need to search on the term "Poisson distribution" to understand things like lambda and mu values. I don't write code in Java but am almost certain that its library will contain something that can be used to generate Poisson arrivals using these values.

You're being asked to create a number of queues, queue processes on them using a Poisson arrival distribution, and collect queue statistics. You're also supposed to do some sort of rebalancing at the end of each interval--however long that's supposed to be. Again, the problem statement is incomplete. But don't bother to post the rest of it without some code to show what work you've done. No one on this site will do your assignment for you, and no one will debug your code if you just post it and say "Why doesn't it work?" But if you post specific questions, someone is likely to help.