You will have been given a deadline. Usually you have to have your report filed within 24 to 48 hours. Be punctual! This could determine whether you will get any future assignments with this company. Most likely you will be able to file your report online or fax it in. Simply follow the instructions you were given. 

It is very important that you be as accurate as possible, giving only the facts requested. If your assignment was to evaluate cleanliness at an establishment, don't make comments about the staff either good or bad. Don't  interject  personal thoughts of your experience unless asked.  

Make sure you have your receipt.  You will need to turn this in for reimbursement. 

The amount of work and time involved depends somewhat on the type of assignment you accept. You might possibly only receive a rebate on your meal in return for filing a 30 question evaluation of a restaurant which required 2 hours of your time.

If you are asked to purchase an item at a gift shop, the shopping experience may require 20 minutes and the time to file your report may take 20 minutes. For such an assignment you might receive reimbursement for your purchase and $20.

File your reports and receipts promptly to ensure you receive payment as promised by the company.