Tasks are an important tool to manage your team and get on overview of all your to-do's. To assign task to a specific user you have different options in Q. to do that:
First of all, you can assign a task to someone while creating a new one. You will find here more about how to create a new task.
If you create a new task there is an option to choose an assignee. When you are creating the task, you will be assigned first. But you can easily change that by clicking on the little "x" next to your name.
Then you can click on the dotted assignee field and you can select one of the employees to assign the task.
When the task is already created and you want to change the assignee you have to go to the task overview. Here you can change the assignee by clicking on the round User Button.