To view night flying you need to select a night time photofield such as Grass Flatlands(night) or a night time 3D flying site such as Flight School(night) or Obstacle Course(night)
With regards to Streamers you add them to the wings of your chosen aircraft using the editor…
from Joe Teibel at Knife edge ...
In the aircraft editor, select the component e.g. wing, fuselage, etc. that you'd like to add the streamer too then select "Add Streamer Component" (it will say, "Add Symmetrical Streamer Component" for components like wings, meaning it will add one to each side) from the Edit menu. If that item is not in the Edit menu, you cannot add a streamer component to whatever component you have selected.
There is also a Yak 54 with streamers fitted already.