Office Space
You Can place a table there and some small shelves. A laptop or a PC will fit in there without any major problems.

If you want to concentrate on your work without anyone distracting your attention you can mount a door. Sliding doors would be the best choice because it’s not going to take up a lot of space, but they can be expensive. Swing doors on the other hand may or may not fit or look appealing.
Ways to use the space under the stairs in the hallway.

The hallway by due to its nature is like a very busy intersection with streets coming from all over the place. This means that this space can be used to store something that has to be at any moment at hand. Depending on what type of situation you are facing and what décor or architecture that space under your stairs from the hallway can be used to expand your décor or as storage area. A very good idea that also comes in quite handy is to transform that space to store your shoes and clothes for the cold\warm season. You can live it open or closed with big doors.
A bookshelf

A bookshelf is perfect for that space because you can make the shelves one longer one shorter one higher one lower and it will look great and I am sure that your favorite books won’t mind. Decorations also can have their “sanctuary” under the stairs as well as electronic equipment embellishing the entire living room with color and texture.
Kitchen

This method of using the space under your stairs is recommended only in very tight situations when the lack of space is really an issue and you already eliminated all the other options. Using the area under your stairs as kitchen or at least a part of the kitchen in my opinion is a bit on the limit because I am a man who likes to cook a lot and when I’m doing that I don’t want any shoe lasses getting in my food not mention dust or dirt.For those who don’t have a lot of space to play with that spot can very easily incorporate some appliances, a sink or a stove. Above that you can put all your plates and coffee cups on small shelves, spices as well.
Rack and shelves under the stairs
We can all agree upon the fact that the easiest way to arrange the space under the stairs is with shelves and racks. A lot of things can be placed there without the need of heavy furnishing. Shelves can and it is actually recommended to be of different sizes and a little bit asymmetrical because the usual square spaces and straight lines don’t necessarily fit in new, modern interiors. On shelves you can store almost anything the only thing that matters is where the stairs are located because different spaces call for different items.

Drawers built under stairs

They had everything organized vertically with distinct drawers for different types of fabric as well for the various types of threads. This is really a good idea if you need extra storage space. Drawers are a little bit more private and you can organize your things better than on shelves, not to mention that on the exterior the entire ensemble of drawers looks really great and adds a bit of sophistication and mystery into the room.
Racks for wine under stairs

Building a rack for wine is not that complicated and the final product filled with different bottles can serve very well as a decorative element.Both the rack and the individual bottles will definitely draw your guest’s attention. This adds a bit of class and elegancy in your décor making it a warm, welcoming house.
Storage under open wooden stairs