before you know it

This phrase means "quickly". You can think of something happening so quickly that it finishes before you notice that it's happening. It's usually used to describe time lengths of months or years that pass by quickly:

Before you know it, you'll be finished with school and ready to find a job.

Summer will be over before you know it.

(someone) is finished with (something)

Use the phrase "finished with" to talk about something that's completed:

Are you finished with that book yet?

Once you're finished with dinner, I have something I want you to help me with.

(someone) is ready to (do something)

The phrase "ready to ___" is very common in English. Use it to talk about whether someone is prepared to do something:

Are you ready to leave?

I love him, sure, but I don't know if I'm ready to commit to getting married just yet.

find a job

"Finding a job" means searching for a job that you are qualified for, as well as being hired. Use "find a job" like this:

It's hard to find a job in this tough economy.