I'm doing job hunting so I'm very busy now :(
I want to work at bunks or insurance companies.
Today, I took a interview at an insurance company.
But today is my first interview in my life, so I didn't tell anything what I want to say.

I'm really mortifying that.

Correct Version:
Job hunting

Reasons:

The verb here is "job hunting" so adding "doing" is incorrect.

I think you mean "banks" here. Banks are the place where you save your money.

You can only work at one place so this would be singular. Add an "an" in front of" insurance company" because it begins with a vowel.

You do not "take" interviews, you "go" to interviews.

Use "an" because "interview" begins with a vowel.

Use past tense here because it already happened. 

When you are writing something, pick a tense (past, present, or future) in the beginning and stay with it throughout. 

"in my life" sounds weird. If you want to emphasize that you have never been to an interview, you can use the word "ever" in the context given.

Use "say" instead of "tell"

See http://dictionary.cambridge.org/us/grammar/british-grammar/say-or-tell for more on that

Don't include "what" because you already have a subject in your sentence. 

Again, use past tense because all of this already happened.

Job Hunting

I'm doing job hunting looking for a job now so I'm very busy now. :(

I want to work at bunks a bank or an insurance companies company.

Today, I took had an interview at an insurance company.

But today is my first interview in my life, so I didn't tell anything what I want to say.

But today was the first interview I've had in my life, so I wasn't able to say anything I wanted to.

I'm really mortifying that. 

I was really mortified. or It was really mortifying.

Be careful of your tense.  Even though it happened today, it's still in the past.

I hope the interview went better than you think!  Good luck!

Job hunting

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Hi mami, that's all I can correct your notebook. Good luck for you! ^^*