The first week brings a lot of forms. This is called onboarding. Do them carefully: mistakes affect your pay and benefits.
Form I-9: proving you can work
Every US employer must check that every new worker, including citizens, may work in the US.
Fill in Section 1 no later than your first day of work.
Show original documents by your third business day. You choose them from the official list: either one document from List A (for example a US passport, a green card, or a foreign passport with the right I-94 or work permit) or one from List B (an ID, such as a driver's license) plus one from List C (for example a Social Security card).
The employer may not tell you which documents to bring, or ask for more than the form requires. That can be illegal discrimination.
If your work permission has an end date, your employer will check again before it expires. Renew early.
Many employers also use E-Verify, an online system that compares your I-9 with government records.
If there is a mismatch, you get a Tentative Nonconfirmation notice. It is often a name spelling or a record that was not updated.
You have the right to contest it. Your employer may not fire you, cut your hours or delay your start while you fix it.
Form W-4: tax taken from your pay
The W-4 tells your employer how much federal income tax to hold back from each paycheck.
Most single people with one job only fill in their name, SSN and filing status.
Nonresident aliens for tax (many F-1, J-1 and new H-1B workers) must follow special instructions. Ask payroll for help.
Some states have their own form.
No SSN yet? You can usually start work; give payroll the number as soon as it arrives.
See Your paycheck: gross, net, W-4 and FICA for what comes out of your pay.
Give payroll your bank's routing number and your account number, or a voided check. Your first pay may come as a paper check while it is set up.
Benefits: the enrollment window
New workers usually get a short window, often 30 days, to choose health, dental and vision insurance, retirement savings (401(k)) and other benefits.
If you miss it, you usually must wait until the yearly open enrollment, often in November, unless you have a life event like marriage or a birth (usually 30 days to change).
Ask HR: "When does my coverage start?" Some start on day 1, others on the first day of the next month.
Using a name that is different from your documents. Use the same spelling everywhere.
Not reading the benefits options and missing the 30 days.
Ignoring an E-Verify mismatch letter. Act within the deadline it gives.