MS Project has a large number of useful pre-set filters, which enable you to focus on particular aspects of your plan. For example, unstarted tasks or overallocated resources.
By default MS Projects filters by All Tasks. To change the filter go to the Project menu Project > Filtered for:
You will see a list of commonly used filters. You can filter by pretty much anything, but I find the Critical and Using Resource filters most useful. Critical shows tasks on the Critical Path and Using resource enables you to view just the tasks allocated to a particular resource. Simply one of the top level filters to apply it to your plan.
If you can't find the filter you need view the full list by going to Project > Filtered for: > More filters
Note that the lists of filters are grouped into those that apply to Tasks and those that apply to resources. Use the radio button to toggle between them.
Click the Apply to see the filter in action!