How long the resume stay posted?

Once you posted your resume by General Info tab then it will always be posted until you update your resume again.

How do I respond to a job?

You can see the job detail after search to any job. There you can simply apply for this job by clicking send resume button. After clicking on that button your current resume and work related detail will be open on popup box. After click on submit button your resume will be sent to employer of this job.

Is there a Job Notification agent and how does it work?

Yes, you can subscribe for Job notification by clicking on Email Notification on Dashboard. You can subscribe by Job category and City. Once you subscribe email notification then all the new posted job detail by these category and within these city which you have selected, .will be come to you by email