Credit Card earned Millages
UA does have a couple of ways to earn PQM (mileage towards status) without flying, but typically, they are earned by flying (and can be earned more cheaply that way).
UA almost always offers an opportunity to buy PQM when you have an upcoming flight with them. In the reservation on the website, there is almost always an ad-style button offering to sell you extra miles for $X. If you click on there, it will offer you two different amounts of mileage you can buy - these are RDM (redeemable mileage only). But if you select one of them, it will offer you Premier accelerator for $Y additional dollars - this will also get you the same amount of miles toward Premier status. Note these are an expensive way to do it - typically, the cost will be between 12 to >20 cents/mile. This can vary based on several factors, including time of year (toward the end of the year, the cost tends to go higher), status it will get you, and potentially more. Typically, the amount of miles you can buy are based on the length of your trip, IIRC, usually 2x or 3x the amount of miles of your trip.
In addition, holders of some legacy cards (which you can no longer apply for) allow earning PQM. For example, I have a UA Select Visa, which gets me 1 PQM for every $ I spend on United's web site, up to 5,000 PQM a year. Other cards get you PQMs for hitting a certain amount of spend per year (IIRC, it's 35,000 though I'm sure someone else can confirm). However, there is no way to get these cards anymore.