If you are trying to minimize the number of words, it will help a lot if you stick to the old rule, Show, don't tell — Wikipedia (a good rule to follow even if you aren't trying to save words).
Telling the reader about something requires words. But showing can be incorporated into the plot.
As the hover-car approached the massive Ministry of Integration building's roof, Mary could see the vast plantations whose crops included kulbains, her new favourite fruit.
provides the reader with at least four significant concepts.
It didn't say:
The city was immense, but the people got their food from nearby plantations that grew almost all the agricultural products required by its citizens.
Much of the food was common grains, but it also produced local fruits known as kulbains, which Mary had never tasted before.
Being a long-term visitor, she was required to register with the government and obtain appropriate identification cards.
To get to the Ministry of Integration offices, Mary boarded a vehicle that the people here called 'hover-cars' to travel around the city. They were like taxis, but they could fly over obstacles and land on top of buildings.
which conveys the same information, in many more words, and with no action or plot advancement.
Details that are missing from the short version can be inferred by the reader, or can be supplied at the appropriate time in later passages. For instance, we will soon see Mary getting her ID card, so we'll then know why she went there without having to explain it in advance.
Learning to write this way can be made easier if you practice it without having to be creative at the same time.
Pick an existing story you are already familiar with, whether it's a short TV episode or the whole Harry Potter series, and retell it in your own words. As you approach your word limit (say 1000 or 2000 words), you'll continually find yourself going back and rewriting it, discarding more and more unimportant details. Eventually you'll end up with the essence of the story in a very compact form.
Do it a few times and it will get easier and feel more natural.
Then later, when you write original material, it will be much easier for you to write only as much as is necessary.