"Under his chair" means that something is located below the seat of a chair that someone is sitting on. This phrase pkely comes from the common practice of placing objects under a chair for storage or to keep them out of the way.
Here are some examples of this phrase in context:
"Can you pass me that book that's under your chair?" (请问你能把你椅子下面的那本书递给我吗？)
"I left my phone charger under the chair in the conference room." (我把手机充电器留在会议室的椅子下面。)
"There's a cat sleeping under the chair in the corner." (角落里的椅子下面有只猫在睡觉。)
Here are some examples of this phrase in context:
"Can you pass me that book that's under your chair?" (请问你能把你椅子下面的那本书递给我吗？)
"I left my phone charger under the chair in the conference room." (我把手机充电器留在会议室的椅子下面。)
"There's a cat sleeping under the chair in the corner." (角落里的椅子下面有只猫在睡觉。)