Yes, you are authorized to work incident to your status as a refugee. To receive
xForm I-766, Employment Authorization Document from the USCIS, you must apply on Form I-765, Application for Employment Authorization.
Yes, while you are waiting for your USCIS issued Employment Authorization Document or a social security account number card, which can also be used to show your work authorization, you can present USCIS Form I-94, Arrival-Departure Document to your employer. When you are admitted to the U.S., the USCIS will issue you the departure portion of Form I-94, Arrival-Departure Document that contains a refugee admission stamp. This unexpired refugee admission stamp will show your employer that you are authorized to work.
However, within 90 days of your hire you will have to present to your employer either an unexpired Form I-766, Employment Authorization Document, or an unrestricted social security account number card together with an identity document that is listed on the back of Form I-9, Employment Eligibility Verification Form, to continue your employment