Hello, Karaageyoukai! Aura's corrections are very good, but since you used semicolons, I wanted to give you some phrasing options that used them as well.

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I ate beef merlot for dinner. Beef merlot is sliced (or cubed) beef steak cooked with vegetables like carrots, potatoes, and green beans in gravy sauce [1] (Mmaybe "wine sauce" because it is merlot? I am trying to describe what I ate without looking at the correct definition).

I have had never known heard of "green beans" until I decided to write this post. This is because, in Japanese, green beans and kidney beans are essentially the same (they are called "Iingen"); [2] but however, there is a slight difference between them;: [3] while kidney beans are called "Iingen," green beans are called "Ssaya-Iingen," meaning = "kidney beans in a (sword) case"." [2]

Words relating to food are still confusing to me,; [3] I need to study harder!

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Notes:

1. "Gravy" is a type of sauce, so "gravy sauce" is redundant. You could use just "gravy," or you could use "wine sauce" or "wine gravy."

2. Capitalizing foreign words is one way to differentiate them, but italicizing them (like Aura did) or putting them in quotation marks are more customary ways. In American English, commas and periods go inside those quotation marks; in British English, the punctuation goes outside the quotation marks. I've corrected your usage to American English punctuation, but your usage would be correct in Europe!

3. Here are some notes and explanations about punctuation. I'm a punctuation nerd, so it got a little long, but I hope it'll be helpful for using the more obscure punctuation marks.

Commas separate phrases or dependent clauses (collections of words that can't make a complete sentence on their own), and they are used with conjunctions. Semicolons separate independent clauses (collections of words that could make a complete sentence on their own); they are not used with conjunctions. Periods separate independent clauses and denote complete sentences. A semicolon looks like a period on top of a comma; you can think of semicolons as a hybrid between the two, joining like a comma but requiring an independent clause like a period.

There are two main exception cases for semicolons. Although semicolons are not used with conjunctions, they can be used with adverbs such as "however," "regardless," and "nevertheless." In English, it's not good form to begin a sentence with "but"; however, it is normal to begin a sentence with a contrasting adverb, and "however" can follow a semicolon even though sometimes it is used like a conjunction. The other exception is for sentences that have a lot of nesting phrases and consequently have so many commas that the meaning is obscured. In such cases, semicolons can be used between phrases as extra-strong commas for clarity. For example, in the sentence "I went to dinner with my mother, an architect, her best friend, an interior designer, and my brother, an amateur magician," it is unclear whether you went to dinner with three people or five. "I went to dinner with my mother, an architect; her best friend, an interior designer; and my brother, an amateur magician," makes clear that you had dinner with three people and that you are giving us information about them.

Colons are usually only seen separating hours, minutes, and seconds in timestamps, but they can be used to introduce a list or to introduce a new clause that elaborates on the previous clause. In the latter usage, they are much like semicolons, but they can be used with phrases, not just independent clauses. When used to introduce an elaborating clause, a colon can be used interchangeably with a single em dash—that long dash that is sometimes used in a pair like parentheses—but a colon is more formal than an em dash; it is primarily seen in academic writing and in British literature from the nineteenth century (e.g. Jane Austen, Charlotte Brontë).

Green Beans

I ate beef merlot for dinner. Beef merlot is sliced (or cubed) beef steak cooked with vegetables like carrot, potato, and green beans in gravy sauce (maybe wine sauce because it is merlot? I am trying to describe what I ate without looking at the correct definition).

I never knew what "green beans" were until I decided to write this post. This is because, in Japanese, green beans and kidney beans are essentially the same. (They are called ingen). Although, there is a slight difference between them. While kidney beans are called ingen, green beans are called saya-ingen (kidney beans in a "sword" case).

Words relating to food are still confusing to me. I need to study harder!

I think you could call it "wine sauce."