The Byers shed is a shack located at the backyard of the Byers house.
It was at this shack where Will took shelter from the Monster before being vanished into an alternate dimension. Later, Will was also interrogated at this place by his friends & family when he became possessed by the shadow monster.
This shed mainly consists of miscellaneous household stuffs and paraphernalia. A hunting rifle is also reserved there.
While returning home after playing D&D with his friends at Mike's house, Will saw a mysterious figure in the middle of the road. It terrified him, causing his bike to crash and compelled him to rush to his home. However, there was no one there and even though he tried to call for help, the phone malfunctioned.As the creature chased and broke in through the front door, Will ran and took refuge in the Byers shed. He unnervingly loaded a gun to protect himself. But the shed's dangling light bulb began to flicker and a strange, guttural growl was heard. Will became stunned to see the monster before he suddenly vanished into the Upside Down. 
Later, when Will's mother and brother left in search for his whereabouts, Dr. Brenner and his agents investigated the shed and traced scans of some supernatural energy, indicating evidences of a portal.
1984After Mike convinced the group to interrogate Will, who was then possessed by the shadow monster, in order to find it's weakness, the Byers shack was completely remodeled. Will was tied to a tool-shed there, who upon awakening failed to recognize the place and so the shadow creature couldn't spy him. Joyce, Jonathan and Mike then share their fondest memories with him in an attempt to snap him out.
Although Will was vocally unresponsive, Hopper soon found out that Will was covertly communicating the instructions in Morse code and tapped out a message-'CLOSE GATE'. However, when the house phone rang, their location was given away as the shadow creature realized their location through Will and despite him being sedated, sent several demodogs to the house.