There are a few ways. The main way is to use the Phone app
Then Select Keypad, and then dial the number, OR press Contacts and pick a contact and click on the Phone icon under there info. You can also use the Favorites list (IF you set one up) OR Recent Calls list.
Under Extras you will find a Contacts App, which is just like the Contacts selection under the Phone app. That too can be used.
And finally you can use Siri to make calls. Siri can call anyone on your contact is as well as dial numbers. She can also look up businesses and ogten call them. "Siri call my wife" will result in a call to your wife, IF you have a "wife" listed in your contacts.