You can earn United Airlines MileagePlus miles by taking flights with United, using United-affiliated credit cards and enrolling in partner programs. Partners include hotels, car rental agencies, retail stores and restaurants that allow you to earn a certain number of miles per dollar spent.
United offers two credit cards that allow the cardholder to earn miles. The MileagePlus Visa card grants 25,000 bonus miles after $1,000 in approved purchases plus 5,000 miles for adding an authorized cardholder, as of 2015. The MileagePlus Club Card allows you to earn 1.5 miles for each dollar spent at retailers and 2 miles per dollar spent at United.
You can also earn miles by using MileagePlus Shopping. While logged in to your MileagePlus account, click to the MileagePlus Shopping page and choose from a number of online retailers, like Sears, Nordstrom, Sephora, The Body Shop and more. Visit the store's website from its link on the MileagePlus Shopping site and earn miles for each dollar you spend.
MileagePlus Dining is a similar program that allows you to enroll a debit or credit card and earn miles for money spent on that card at participating restaurants. You can also earn miles through partner programs with financial services companies and utility companies, and by taking surveys through the Opinion Miles Club.