Its easy enough to specify how many hours a resource works and that is defined by the Max Units on the Resource Sheet. A Max Unit value of 100% is full time or for the Standard calendar, 40 hours/week.
Its also easy to specify how long a task will take but "how long" needs to be defined. The time span during which a task is performed is specified by the Duration field. The amount of effort to complete the task is specified by the Work field.
There is no field in Project that equates to how many tasks need to be completed in a given time frame. That's a metric you have to decide and monitor.
Project will not plan the work for you but there is one way to see how many resources are required to do a given amount of work in a specified time frame and that is by setting the Task Type to Fixed Duration. In this example the resource "Joe" has a max unit level of 100% (i.e. available to work 40h/wk). Task 1 is defined to take one week (duration). Initially, Joe is assigned at 100% so the work content is 40h.
Now let's say the work content is increased to 80h for that one week task. Note that Project calculates a Peak assignment value of 200% meaning it will take 2 resources to complete that task, assuming the second resources is also available for 40h/wk.
Hope this helps.
John