Gemini/Cancer Cusp

I'm new to astrology, so I don't really know how "cusp babies" work. My friend was born a Cancer (June), but I see nothing but Gemini in his personality. If I'm not mistaken, that could mean his exact bday is on the "cusp" of the two signs? What does that mean?

Also curious about my brother: he's born a Leo (I'm July 19, he's July 24), but I see nothing but Virgo in him, and I've always known him to be a very introverted person, even more so than me in many ways! Totally nowhere near the cusp, but maybe he just has a lot of Virgo in other planets? Neither he or I know his charts.

Your brother is a Leo.

You haven't said what the rest of their placements are.

I have a good Cancer friend with a Gemini moon and mars. She comes off like a Gemini through and through. Although sometimes I get the impression that she's hiding behind all that energy.

My best friend's ex-boyfriend is a Leo sun, moon w/ a Virgo venus, mars and he was really quiet and reserved.

My absolute favorite, awesome guy friend is a Gemini w/ a Pisces moon and mars. He's most definitely an exuberant, crazy Gemini, but it takes him a while to warm up to people and show that side of him.

I'm a Taurus/Aries cusp, but I don't really notice any Aries traits.

I'm on Gemini Cancer cusp; born 21st June evening. For a long time I considered myself as a Gemini due to my lively appearance (Mercury Gemini). I've always enjoyed solitude and I can be somewhat moody and even snappy if something/someone pushes my buttons with unthoughtfulness, bad comments, rude behaviour etc. A few years ago then I did an astro map, and realized I was actually more a Cancer than Gem; I am really emotional, sensitive, (Sun&Moon Cancer), stay-at-home -person (though I travel for work -> Asc Sagittarius). Me being a Cancer makes much sense, though I feel I become quite Gemini-like when I drink 😉 I say it depends a lot on the other placements on one's astro chart.