The way we created a bug, in the same way we can create a task in Jira by clicking the create button.

For example a developer lead can create a task to create a login page.

He can give some summary, description, assign it to a developer and add a functional specification document in the attachments.

The assigned developer can change the workflow from to-do to in Progress and after finishing the task it can be changed to done. The developer can even add some comments etc.

Everything can be seen by going to the activities tab.