Adorno argued that capitalism fed people with the products of a 'culture industry' - the opposite of 'true' art - to keep them passively satisfied and politically apathetic.
Adorno saw that capitalism had not become more precarious or close to collapse, as Marx had predicted. Instead, it had seemingly become more entrenched. Where Marx had focussed on economics, Adorno placed emphasis on the role of culture in securing the status quo.
Popular culture was identified as the reason for people's passive satisfaction and lack of interest in overthrowing the capitalist system.
Adorno suggested that culture industries churn out a debased mass of unsophisticated, sentimental products which have replaced the more 'difficult' and critical art forms which might lead people to actually question social life.
False needs are cultivated in people by the culture industries. These are needs which can be both created and satisfied by the capitalist system, and which replace people's 'true' needs - freedom, full expression of human potential and creativity, genuine creative happiness.
Commodity fetishism (promoted by the marketing, advertising and media industries) means that social relations and cultural experiences are objectified in terms of money. We are delighted by something because of how much it cost.
Popular media and music products are characterised by standardisation (they are basically formulaic and similar) and pseudo-individualisation (incidental differences make them seem distinctive, but they're not).
Products of the culture industry may be emotional or apparently moving, but Adorno sees this as cathartic - we might seek some comfort in a sad film or song, have a bit of a cry, and then feel restored again.
Boiled down to its most obvious modern-day application, the argument would be that television leads people away from talking to each other or questioning the oppression in their lives. Instead they get up and go to work (if they are employed), come home and switch on TV, absorb TV's nonsense until bedtime, and then the daily cycle starts again.