When opening Unity, you are given the choices to start a new project, open an existing project, or watch a getting started video, as shown here:
To get started, let's create a new 3D project. Name it AR_is_Awesome or whatever you'd like as shown ahead:
Fill in the name for your project and verify that the folder location is what you want. Ensure that 3D is selected. There is no need to select any extra asset packages at this time. Click on Create Project.