Hello, everybody! Today, I'm going to talk about points in times a bit.
いますand あります are pretty standard verbs and some of the first words for newbies. In a nutshell, they both mean "to exist", where います is for animate objects and あります is for inanimate objects, or rather non-living things even including events and plans. They also have secondary meanings: います also means "[Verb]-continuously" and あります also means "to happen". We're going to talk about the latter meanings today, and how it relates to another verb, おきます.
おきます/おく is a verb commonly meaning "to put/place", but it has a bunch of other meanings too. We're going to talk about the particular meaning of "doing something in advance".
Usually, 〜ています is taught early and alone, because it has a pretty common equivalent in English. It means to do a Verb continuously, or in simpler terms "~ing".
[I'm] playing a video game.
When you want to put a verb into ~ing form, you need to put the verb into its て-form and put an います at the end.
Even in English, there is a noticeable difference between "I eat sushi" and "I am eating sushi". The former is a very general statement presented as a fact, while the latter describes the current action at a specific time. Imagine this phone conversation:
Ｂ：「はい、すしを食べます。今、すしをたべています。」
A: "B, can you eat sushi?"
B: "Yes, I eat sushi. I'm eating sushi now."
Even unconsciously, you can see how B's first and second statement portray different things.
Now, 〜てあります isn't the 〜ています when it comes to inanimate things. It has a meaning that can also be applied to living beings. 〜てあります is a little difficult to explain and it's often explained with ~ておきます. The best way I can think of explaining the two of them is that ~ておきます is to do something in advance, while 〜てあります is to create a continuous situation. Unfortunately, they're kind of similar in usage:
I threw in the first sentence just for comparison review.
I'm buying a cake for the party.
I [have presently] bought a cake in advance for the party.
I [have presently] bought a cake for the party.
I realize I have made this more confusing by putting the last two sentences in past tense when the Japanese tense is clearly present, which is why I threw in "have presently", because while it is heavily implied in Japanese, it's a little wordy in English, and it makes more sense this way.
The point of Sentence #2 is to describe a particular action, also emphasizing that the cake was bought prior to. This is a single moment in time. The point of Sentence #3 is to describe the situation of now having the cake, and the cake is still around. This is an ongoing moment in time. Next example:
そのレストランに行きたいから、よやくしております。
そのレストランに行きたいから、よやくしてあります。
I want to go to that restaurant, so I already made a reservation.
I want to go to that restaurant, so I have a reservation.
Again, sentence 1 is describing having previously done that action of making a reservation, and sentence 2 is describing the situation of having a reservation.
〜ています: Used to describe an action currently being done [いま]
〜てあります: Used to describe how an action creates an ongoing situation [いまから]
~ておきます: Used to describe how an action is done in advance [あとのために]
Bonus Round time: That being said, I want to briefly go over the difference between 〜てあります and just あります.
I have bought ice cream (which is still around).
Again, slightly different pictures. The first sentences doesn't describe any particular action, just that ice cream is, well, here. The second sentences makes it clear that the ice cream was bought (I suppose rather than home-made or stolen), or even "There is ice cream that I bought":
This is wordy even in Japanese, and even requires the use of passive form and descriptive verbs. The previous sentence is much less wordy and more natural.
