As mentioned here, you can easily create your own certificate template, which specifies what your certificate will look like.
You can go to Studio and hit Certificates and go straight to the tab 'Certificate Templates'. There you will have an overview of all the templates that are already available. To create a new one, hit the top right button 'New Certificate Template'. You can first name your certificate, this will however not appear on the certificate itself, it is simply meant for reference. You could for example call it 'Simple Template' or 'Detailed Template', depending on the kind you're creating.
You can now select how in detail you want your certificate and which elements you want on there. You can simply turn the items on or off. After creating your template, these fields you've selected will automatically be filled in, with the details of the course, session and student. Additionally you can set a background for your certificate as well.
When done assembling your certificate, simply press 'Save changes' and your certificate template will be available to use!