The difference between global and personal templates is that global templates are available for all users, where personal templates are only available for the user who created them (comparable to issue filters).
Global Templates
To create a global template please navigate to the app administration and choose Global Templates.
By clicking on Configure you can now define your template. Fill all fields with values, that should be pre-filled in the template. Example:
Personal Templates
To create personal template, navigate to your user profile (click on your profile picture in the upper right corner) and choose Issue Templates. You will see the following screen which will show all global and personal templates after you created them. But first click on the edit button to create a new personal template.
Give your template a name and choose a project where it should be applied. This means that issues created by this template will be created only in this project. After saving click on the action button and choose Configure. Now you can configure your fields:
After saving you can find your template in the overview. If you now click on your template, a create screen will open and you can create issues by using your template.