そろそろ行きましょう とはどういう意味ですか?

そろそろ行きましょう simply means "time to go? time to leave? Why don't we leave or go?"

In that context, そろそろ represents "time is coming", 行きましょう is like why don't we leave or go.

It changes meanings depending on a situation.
If you are with a friend, it would be just a suggestion.
If you are with your supervisor, it would be almost a command, so you have to do that.

うーん、なかなか説明するのは難しいですねw
付け加えて質問あるんでしたらまたお答えします！