Go here: https://duckduckgo.com/spread (copy / paste the link for it to work).
Scroll down to the bottom and click ‘Show Me How’.
Register for an account.
After you make an account log in and answer the 3 questions.
In the next 30 days, spread the word about DuckDuckGo (there’s no tracking link or anything).
After 30 days, sign in and answer a few questions about how you got them to switch and claim your FREE t-shirt.