at this point on a project I only have resource man hours but I do not know the who is working on what activity just total man hours for activity has been given. How to I assign man hours to all activities? Also I have total overhead cost for all activities how to assign that to all activities in total in MS Project.
Resources can be groups of people: engineers, QA, etc. Create resources where the name is the type of worker, not the name of a specific worker and assign those to the tasks. Then you look at the resource usage view to see how many man-hours you need each week for each type of worker.
Use a numbered cost field such as Cost1 for overhead cost. To combine with resource costs, use the Cost2 field and customize it with a formula
=[Cost] + [Cost1].
Define roles rather than people. Unless it matters that "Sally" does the work instead of "John," you can use roles like developer, tester, architect, engineer, machinist, or whatever other skills or job titles the work requires. You might also consider using teams rather than roles or people, if your teams break along functional lines.