Once you have hired someone and would like to close the job, simply deactivate the job.
When you first log in, click on the 3 dot menu of the job opportunity and choose Deactivate Job.
Deactivating a job while reviewing candidates
If you are still evaluating candidates but no longer want to receive new candidates, simply disable the job application page.
Click on the settings wheel of your job, scroll to the bottom and select the option "Disable candidate access to job application page" and save.