1. I made Harry Porter interesting by adding more stories.

(is this sentence grammatical?)

2. We shook the building, and it fell dowm. (Is this grammatical?)

3. I will give some hints to you?
(What does 'hints' refer to? What are other similiar expressions?)

1. fine

2. ok. In the old days, when I was in school, we had to put a semicolon ( ; ) between such phrases that are complete as sentences. By the way you misspelled down. I might use two sentences:
We shook the building.
It fell down.
3. hints is the object of the verb, does not refer to anything as far as I know.

1. The sentence "I made Harry Porter interesting by adding more stories." contains a grammatical error. The correct spelling is "Harry Potter," not "Harry Porter." Additionally, the word "interesting" should be changed to "more interesting" to convey the intended meaning. A revised version of the sentence would be: "I made Harry Potter more interesting by adding more stories."

To determine if a sentence is grammatically correct, you need to review the rules and conventions of grammar. This can involve looking at elements such as subject-verb agreement, correct verb tense, proper use of punctuation, and so on. Grammar guides and resources, including grammar books or online guides, can be helpful in understanding and applying the correct rules.

2. The sentence "We shook the building, and it fell dowm." contains a grammatical error. The word "dowm" should be corrected to "down." A revised version of the sentence would be: "We shook the building, and it fell down."

Again, to check the grammatical correctness of a sentence, you need to consider grammar rules and guidelines. In this case, it involves proper spelling and usage of words.

3. The phrase "I will give some hints to you?" is grammatically correct, but the question mark is unnecessary. Hints refer to clues or suggestions provided to help someone understand or solve a problem. In this context, it means that the speaker will provide some suggestions or clues to the listener. Similar expressions that can be used instead of "hints" include: tips, pointers, suggestions, guidance, or advice.

Understanding the meanings and usages of different words and expressions can be done through various resources, such as dictionaries, thesauruses, or context-based learning.