Not only do we need oxygen to breath on Mars, we also will need to produce rocket fuel to take off again.

In fact the article says we would need 31 tons of oxygen. The Mars atmosphere is thin, but it contains CO2.

The Mars Oxygen ISRU (In-Situ Resource Utilization) Experiment is a box that is about 40 lbs and the size of a toaster. It has shown that it can produce oxygen day and night through a wide temperature range.

The current unit produces 6 to 8 grams of oxygen per hour. You need about 3 times this much for a human to breath. A larger version of the unit, at 2 to 3 kg per hour, could generate enough fuel for lift off in about 26 months.

MOXIE Shows How to Make Oxygen on Mars – Results from a test unit aboard the Perseverance rover have scientists optimistic for future crewed missions