~ていた
Something was happening in the past
You'll be able to describe an action or continuing state that was in progress at an earlier time.

蓮は部屋でギターの練習をしていました。
ren wa heya de gitaa no renshuu o shite imashita.
What do you think this sentence means?
Ren was practicing guitar in his room.
Look back at an ongoing action or state
~ていた is the past of ~ている. It describes what was happening, a state that existed, or a repeated habit at a past time. The verb and context determine the interpretation.
窓が開いていました。
mado ga aite imashita.
The window was open.
Form and use ~ていた
With an action such as reading, it can mean “was reading.” With a change verb such as 開く, it describes the resulting state: 開いていた means “was open,” not continuously opening.
窓が開いていました。
mado ga aite imashita.
The window was open.
去年は毎日走っていました。
kyonen wa mainichi hashitte imashita.
Last year I used to run every day.
昨日電話をもらったとき、お風呂に入っていました。
kinou denwa o moratta toki, ofuro ni haitte imashita.
When I got a phone call yesterday, I was in the bath.
朝起きたとき、外は雪が降っていました。
asa okita toki, soto wa yuki ga futte imashita.
When I got up in the morning, it was snowing outside.
家に帰ったとき、部屋の電気がついていました。
ie ni kaetta toki, heya no denki ga tsuite imashita.
When I got home, the light in my room was on.
7 more examples in the grammar path — free for a limited time.