Defects or Bugs are just another issue type in Atlassian JIRA like stories and tasks.
“Defect” issue type is required in development project to capture any anomolies during the SDLC and then to rectify those in order to meet user expectation.
Logging defects in JIRA is similar to creating any other issues. The defects will have different templates and can follow different workflow as compared to other issue types.
The following video explains the step by step process to log a defect in JIRA.