What does しています mean?


TL;DR what does している mean, or what can it mean given various circumstances?
What are its limits of use?

I am confused on the meaning of the verb する plus the ている ending. I know する has
many meanings such as "to do" or "to wear." However, I am always confused how
to interpret している; it seems a little weird. It can be used to mean to have or
not to have, as in a part-time job (いいえ、アルバイトをしていません). I think it can be used
to mean "wearing," such as どの人が黒いTシャツをしていますか, but since I made this sentence I
am not sure. It can also refer to something you are doing, like いま、なにをしていますか.

Since I do not know exactly what しています refers to I find it hard to use in
various situations and sentences. How do you personally interpret and make
sense of しています as the verb する plus the ている ending in sentences? How can you
use しています if it has so many meanings, and how do you know when it can be used
and when it does not make sense?

In the genki textbook, する just means "to do," so maybe that is where the
confusion caused by its many meanings is coming from for me...




しています is a combination of する and -ている (or -ています in polite form), both of which
are difficult topics.

### Meaning of する

You seem to understand this, but [する has many
meanings](https://jisho.org/word/%E7%82%BA%E3%82%8B). Basic verbs like する, やる,
とる, かける, みる and so on have many possible translations, and you cannot
understand them just by thinking of a single translation. The same goes with
English; you may think _take_ is an easy verb, but to a foreigner, _take_ is a
really difficult verb that [must be translated in dozens of different
ways](https://dictionary.goo.ne.jp/word/en/take/). You have to accept such a
fact and learn each usage one by one.

### Meaning of -ている/-ています

Fortunately, the -ている ending basically has only three meanings:

  1. is doing now (progressive)
  2. has done (perfective)
  3. do on a regular basis (habitual)

For details, please read these two questions: [When is Vている the continuation
of action and when is it the continuation of
state?](https://japanese.stackexchange.com/q/3122/5010) and [Habitual
aspect](https://japanese.stackexchange.com/q/11925/5010)

For example, 部屋の掃除を **しています** is a sentence that, depending on the context,
means:

  1. I am cleaning the room (now)
  2. I have cleaned the room (so the room is already clean)
  3. I clean this room (regularly) / My job is to clean the room

今何をしていますか only means "What are you doing now" because it clearly says 今
("now"), but 何をしていますか by itself can have a habitual meaning, "What do you do
(as an occupation)?".

Similarly, アルバイトをしていません is _usually_ habitual; it typically means "I am not a
part-time worker" rather than "I am not working part-time (right now)".

指輪をしています is _usually_ perfective; it describes the state of having a ring on
your finger, because wearing a ring is usually an instant process.

