how to assign task to several people?

we need to let some person do the same task together.

Hello Sunny,

you can only assign tasks to a single person or group.

By assigning a task to a group, all members of the group are notified. In effect, you therefore assign the task to multiple users.

in this case, can we cc the task to some people together and notice them by email?

You can add users as watchers to work packages. They will then be notified about any updates by email.

When you open a work package, you will find a "Watchers" tab. You can simply select a project member as watcher.