A person who is "qualified for" a job is someone who has the skills and experience to do the job. Most employers require that someone have a certain educational background or a certain number of years of experience.
When you're talking about whether a person is qualified, you describe them as "a qualified ___". For example:
The school system has an urgent need for qualified math and science teachers.
In general, when you want to talk about the people who are applying for a job, use the phrase "qualified candidates". A "candidate" is someone who's being considered for a job:
Quite a few qualified candidates have applied, so we may not get back to you for a few weeks.