You can make a record of the open vacancies in your company using Job Opening.
To create a new Job Opening go to
Human Resource > Recruitment > Job Opening > New Job Opening
ERPNext allows to plan your recruitment at a group company level. The number of Job Openings you can create for a Designation is restricted according to the Vacancies planned by the Staffing Plan defined for the company or one of it's parent group companies in the hierarchy. To understand how you can do configure this, check Staffing Plan
Next: Leave Allocation