Summer was previously a student of Beacon. She graduated from the school with Team STRQ.
Summer was the leader of Team STRQ.
Ruby is Summer's daughter. Ruby states in "Ruby Rose" that her parents taught her to always help others, referring to Summer and Taiyang. According to Yang, Ruby was also devastated by the loss of Summer, but she may have been too young at the time to fully comprehend the situation.
Ruby still routinely visits Summer's Gravestone, doing so in the "Red" Trailer, in "Round One" and in "End of the Beginning". Ruby apparently finds solace in speaking to her mother, updating her on the events of her life and her feelings, and evidently lamenting her absence.
In "Our Way", Summer appeared during Ruby's flashback.
Summer is Yang's stepmother, and until after her death, Yang was evidently unaware of the fact Summer was not her biological mother. Yang spoke highly of Summer, referring to her as a sort of "super-mom" for herself and Ruby. In "Witch", Yang snaps at Salem for taking Summer from her, specifically refering to her as "Mom"; showing just how much Summer was loved by Yang.
Nothing is known of their relationship during their time at Beacon but following the disappearance of Raven Branwen, Summer and Tai apparently entered into a relationship that resulted in the birth of Ruby. She also acted as a mother figure for Yang.
After Summer's death, Yang said that Taiyang "shut down", devastated by the loss, showing that he and Summer were extremely close and that he greatly misses her.
It is unknown if the two were ever married, though the fact that they lived together and raised Ruby and Yang in their early years indicates they might have been married, however Ruby may have simply been born out of wedlock.
It is unclear what relationship the two had between each other, but both were teammates along with Qrow and Taiyang.
During the Battle of Haven, Raven cynically notes that Ruby sounds just like Summer for wanting to work together, implying some tension between the two.
Qrow was Summer's teammate and while not much is known about what relationship the two had between each other Qrow seems to remember her fondly referring to her as "special" and was aware of Summer's lineage as a silver-eyed warrior.
During a conversation with Ruby in "Pomp and Circumstance" Qrow says that he believes that even upon learning about Salem being immortal Summer would have pressed on like her daughter, he also describes her as "the best of us" while also saying that she could be a brat at times but that he likes brats, indicating a close bond between the two.
Salem's Inner Circle
At some point prior to the start of the series, Summer encountered Salem, having seemingly discovered her immortality and failures, where she claimed that she'd stop Salem.
What happened during the encounter is unknown, but it was implied that Salem is possibly responsible for her death and that the encounter was memorable enough for Salem to distinctly remember it.