Creating an Issue Template is easy.
Go to Project Settings → Apps → Issue Templates
Click on Add Template and an add template window will open.
You can currently add one template per issue type. The template name and issue description fields are mandatory, whereas the summary field is optional.
Using Issue Templates
Once Issue Templates are created, they will be automatically applied and pre-filled for all users when they try to create a new issue from the Create button on the top menu.
If users change the issue type, the corresponding template will be applied.
If you want to deactivate a template, simply go back to project settings and delete the template.
Use action button (…) to edit the existing templates or delete them entirely if a template is no longer needed.
These templates above are limited to one project. If you are looking for reusable templates across projects, please refer to Global Issue Templates.