Ruby is (sort of) the main character. The story mostly follows her and her team as they navigate the world of Remnant.
Ruby is one of the youngest Huntresses to be accepted into Beacon. At only 15 (two years before she was set to graduate combat school), she was offered entrance into Beacon by the headmaster himself, Professor Ozpin. This was due to her exceptional combat ability while thwarting an attempted robbery on a dust shop she was visiting. Though, this is up for debate considering how Ozpin works. There's definitely way more to his reason in letting her join Beacon.
Ruby has an older half-sister named Yang who she's on a team with. The two are very close; Yang is a bit of a mother figure to her since their mother, Summer Rose, died when they were little. The two lived with their dad, Taiyang, up until they were accepted into Beacon. They were also partially raised by their uncle, Qrow, who is the twin brother of Yang's birth mom. Ruby and Qrow are very close, getting most of her fighting style from him. He's the reason she's so proficient with a scythe at such a young age.
Ruby's weapon is a scythe that is also a high-caliber, high-impact sniper rifle ("It's also a gun") named Crescent Rose. Ruby's weapon is special in that only someone of her and her uncle's skill can use it. A normal Huntsman couldn't even begin to handle the recoil on it. Ruby uses the recoil to her advantage, moving around the battlefield at top speed without even using her semblance. Her weapon can transform to be compact so she can carry it around better, to be a scythe which is how she normally uses it, and to be a sniper rifle which is useful for long-distance combat. Ruby is very attached to her scythe, almost treating it like her child (except in V9 when her PTSD was so bad, she couldn't even hold her weapon.)
Her semblance (aka her own personal superpower) is called Petal Burst. When the show was first released, all you could gather from her semblance is that Ruby could move at high velocity in a burst of rose petals. Ruby also believed her semblance was a normal speed-type semblance. However, in V7-8, we learn that her semblance is not like most of the speed variety. Penny, Ruby's best friend, finally explained that Ruby is able to break herself down to her molecular components, negating her mass, and then reassemble herself at her target location. With practice, she was even able to use her semblance on other people, allowing them to move with her. She can also negate gravity, activating her semblance mid-fall in order to bring herself back up. This kind of makes it seem as if she's flying around. However, if there is an obstacle mid-flight, her semblance will deactivate, causing her to fall. This can also happen if she's running low on aura.
Ruby's eye color is special. She has silver eyes which is insanely rare. They're hereditary, Ruby getting them from her mother. Those with silver eyes are destined to be warriors, but it's much more than that. Their eyes are actually a gift from the God of Light which can destroy the creations of the God of Darkness. When Ruby uses her eyes on Grimm, she can completely obliterate them depending on the size and how practiced she is. Silver eyes are like a mirror, reflecting the light of the world onto darkness.
Ruby is an amazing character. The transformation she goes through throughout the series is incredible. She starts off as a goofy and immature girl before turning into a capable leader and strong warrior. She lost so much and hit her absolute lowest to the point where she tried to kill herself, but luckily, she was in a different world where dying is basically just going to therapy to work shit out and be reborn as who you need to be. She finally decided that herself was good enough and that her failures will only make her stronger.
When RWBY released, I was the same age as Ruby in the show. It felt like I grew up with her. She, along with the rest of Team RWBY, are comfort characters for me. Ruby's not my all time favorite RWBY character, but she is most certainly NOT my least. I love this girl and getting to watch her grow as a person and a fighter has been amazing. I could never hate Ruby; she's just a cute bean.