you'd be surprised how (adjective) it is to (do something)

Use this phrase when you're telling people about something they don't know about. If you know some information that you think they won't expect, you say "You'd be surprised how ___ it is to ___". For example:

You'd be surprised how expensive it is to put your kids through private school these days.

You'd be surprised how easy it is to get help with your job search if you just ask around.

There are also some shorter versions of this. When someone makes a guess about something that you know about, and their guess is wrong, you can say, "You'd be surprised."

A: There aren't that many people in Seoul who speak English, are there?

B: Oh, you'd be surprised.

"You'd be surprised to...." is usually used in spoken English, not often in writing.

it's hard to (do something)

When you want to say that some action is difficult, you say "it's hard to ___":

It was really hard to hear what she was saying.

It's hard to know what to do in those kinds of situations.

In the example at the top of this post, "it's hard to ___" was re-ordered to "how hard it is to ___". That's because it was used in the expression "you'd be surprised how ___ it is to ___".

a qualified (job title)

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.