To convey that ‘(A) was happening’, or that somebody ‘was doing (A)’ in Japanese, ていた (or ていました) will be used. ていた is a construction which uses the conjunction particle て, and the godan verb いる (to exist), in its past tense form いた.

• シャワーが壊（こわ）れていたから2日間（かかん）もシャワーを浴（あ）びれなかった。
  Because the shower was broken, I was not able to take a shower for 2 days. (Was in the state of being broken)
• 昨日（きのう）は夜遅（よるおそ）くまでカラオケで歌（うた）っていたので、のどが痛（いた）いです。
  I was singing until late last night at karaoke, so my throat hurts. (Was doing karaoke)
• 昔（むかし）はパーマをかけていました。
  In the past, I used to have my hair permed. (Was getting perms)
• 窓（まど）が割（わ）れていました。
  The window was smashed. (Was in the state of being smashed)

Sometimes ていた is used to express things that are still ongoing, but the speaker is not sure about, or would like to politely advise the listener about. This is very similar to the way in which English uses ‘(A) was doing (B)’.

• お父（ちち）さんがその椅子（いす）に座（すわ）っていたから、こっちに座（すわ）りな。
  Dad was sitting there, so sit here please.

In this example, although the action of ‘sitting’ is not finished, we can imagine that the speaker is suggesting that ‘dad was sitting here, and he still is, but he just went to get a drink’.
The same kind of sentence could be used when the speaker has walked away from where their dad was sitting, and doesn’t actually know if he is still sitting there or not.