1to turn something over or lay it face down; to place something with its face downward.
皿を伏せて乾かしておいてください。
Please turn the plates face down to dry.
手札は伏せて山に置くルールだ。
The rule is to place cards face down on the pile.
写真を伏せて箱にしまった。
I put the photo face down and stored it in the box.
2to cast one's eyes or head downward; to lower one's gaze; to look down.
恥ずかしそうに彼女は目を伏せた。
She looked down, seeming embarrassed.
先生に叱られて生徒はすぐに目を伏せた。
Being scolded by the teacher, the student immediately looked down.
彼は黙って目を伏せていた。
He remained silent with his eyes cast down.
3to lie (one's body) face down; to lie flat on the ground (intransitive use).
犬が床に伏せて眠っている。
The dog is lying face down on the floor, asleep.
警官の指示で容疑者は地面に伏せた。
At the officer's command, the suspect lay face down on the ground.
疲れてソファに伏せてしまった。
I was so tired that I flopped face down on the sofa.
4to conceal or hide something; to keep secret; to place in hiding (e.g., troops for an ambush).
彼は本当の理由を伏せていた。
He kept the real reason to himself.
証拠を伏せるのは許されない行為だ。
Concealing evidence is an unacceptable act.
敵に気づかれないように兵を伏せた。
They concealed the troops so the enemy wouldn't notice.
5to lie down or go to bed due to illness; usually written 臥せる — a somewhat literary/old-fashioned term for being bedridden.
母は高熱で臥せている。
My mother is bedridden with a high fever.
彼は風邪で数日臥せていた。
He was laid up in bed for several days with a cold.