On all pages within your database, you'll see a Search Box in the upper right corner:
You can use this search box to pull up all contacts in your database by clicking within it and then hitting enter on your keyboard. Or, you can search for specific contacts.
You can also search a handful of other fields within your database using this Search Box. Those fields are:
Tax ID Number
You can always get a quick reminder of which fields are searchable here by placing your cursor over the box, at which point you'll see the below: