1Here; this place (near the speaker).
ここが私の部屋です。
This is my room.
ここに座ってください。
Please sit here.
その箱はここに置いておいて。
Leave that box here.
ここから駅まで歩いて十分くらいです。
It's about a ten-minute walk from here to the station.
2At this point / now — referring to the current moment or situation under discussion.
ここで重要なのは準備です。
What matters here is preparation.
ここが問題の核心だ。
This is the core of the problem.
ここはもう諦めるしかないと思う。
I think at this point we just have to give up.
3Used before a duration to mean "these past ..." (e.g. ここ三年 = the past three years).
ここ三年で会社の方針が大きく変わった。
The company's policy has changed a lot over the past three years.
ここ数ヶ月は忙しくて休めなかった。
I've been too busy to rest for the past few months.
4Used before a duration to mean "the coming/next ..." (e.g. ここ一週間 = for the next week).
ここ一週間は出張が続きます。
I'll be on business trips for the next week.
ここ数日、天気が崩れるそうだ。
The weather is supposed to turn bad over the next few days.