Going back a bit (OK, quite a lot):
From birth, and the identification of sex-class membership that happens at that moment, most female people are raised to be passive, submissive, weak and nurturing, while most male people are raised to be active, dominant, strong and aggressive.
Others have covered clothes and their slogans comprehensively, which is one of the more blatant manifestations, but there are a lot of more subtle ones going on when you start looking out for them.
Boys and men being praised for 'leadership' and 'directness' while the same behaviour in girls and women is described as 'bossy' and 'aggressive'.
Schools seating disruptive boys next to girls for their 'calming influence'. Adults making small talk with children tend to compliment a girl on a pretty dress/hair/shoes, but with boys are more likely to ask questions about activities or interests.
The language that people are expected to use - if you look at work emails the ones from men tend to simply state what they want and add a single thanks at the end, while those from women are peppered with please and sorry and just checking and would you mind? I edit a lot of manuals and technical info written by women and even those are full of 'please' when there should be a direct instruction. But if women write emails or comment on documents like men they are perceived as abrasive and (in the case of at least one of my friends, who is a lovely person and always polite and professional) sent on courses to improve their attitude and communication skills.