What does it mean when a employer asks for me to bring my I’d and my social security card?

If this is the United States, you are required to bring such identification before you start. So, this is actually likely a good sign.
Specifically, what the employer needs those IDs for is that they are going to fill out an "I-9 Form" which is a US government form in which the employer (with you) needs to fill-out that they have documented evidence that may work in the United States. (So, illegal aliens who work in the US... Their employers are not filling out I-9 forms for them or are faking it.)
This is an I-9 form.
https://www.uscis.gov/i-9
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US IMMIGRATION AND NATURALIZATION SERVICE
TITLE: I-9, Employment Eligibility Verification
Use Form I-9 to verify the identity and employment authorization of individuals hired for employment in the United States. All U. S. employers must properly complete Form I-9 for each individual they hire for employment in the United States. This includes citizens and noncitizens. Both employees and employers (or authorized representatives of the employer) must complete the form.
On the form, an employee must attest to his or her employment authorization. The employee must also present his or her employer with acceptable documents evidencing identity and employment authorization. The employer must examine the employment eligibility and identity document (s) an employee presents to determine whether the document (s) reasonably appear to be genuine and to relate to the employee and record the document information on the Form I-9. The list of acceptable documents can be found on the last page of the form. Employers must retain Form I-9 for a designated period and make it available for inspection by authorized government officers.
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This has the instructions which you don't really need to worry about too much. If you have a social security card and a driver's license with picture and/or birth certificate or a passport you are good to go. However, what the form needs are identification documents which say 1) identify you and 2) identify that you can legally work in the USA. So, for instance, if you are a US citizen, you are good to go, but you need to prove that. The BEST way to prove that you are you is with a US Passport.
Take a look at the list of List A documents and List B documents and List C documents in the instructions.
www.uscis.gov/.../i-9instr.pdf
It means that after your application you made the first cut. No one is going to waste time granting an job interview unless they know you are here legally. They need to see documentation in order to move along in the hiring process.
That needs they may run a background check on you to verify you are who you say you are. That could mean they are adding you into their system to make you an employee
If you pass the background check, I am sure you will get the job
It’s usually to verify identity and employment authorization. You may also have to fill out a I-9 form
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They may invite you to compete a job application. If you have already completed the application they may make job offers immediately following the interview and they need these documents to begin onboarding.
I have already completed it online does that mean they might hire me on the spot
It's possible.
He wants to hire you. He needs those document so for the I-9 and W-4
He needs to know you are who you say you are and have legal status to be here.
You need it for paperwork and for tax purposes and for your 401k stuff.
Or he wants to maks sure you are legal before he films your first porn seen.
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