I have many questions haha

I am trying to make complicated and natural sentences.

>> I have a lot of questions since I am trying to make complex and more common sentences.

Example
the man who standing on the desk have ate Red apple for ten minutes, watching people around him

>> The man, who was standing by the desk and has been eating a red apple for ten minutes, was watching the people around him.
What is more natural between long sentence and short sentence?
Is it helpful that try to make long sentences?
>> Which would be more natural: long or short sentences? Would longer sentences be more helpful?

Plz select one of them and compare them

>> Please compare and contrast which of these are better.
Today afternoon vs This afternoon

>> "This afternoon" is the correct one because you are in the present tense. "Tomorrow afternoon" and "yesterday afternoon" is correct but it just isn't done for "today"
Do you know it. Have you heard it??

>> "Have you heard of..?"and "Did you know...?" depends on what your sentence is. If you are relaying the latest news then use "Have you heard of..?" but if you are gicing trivia to someone you use "Did you know..."

For example:

Have you heard of what happened between the S.Korea team and the Kuwait team in the last soccer match?

Did you know that eating chocolate gives the same feeling as falling in love?

It isnt to improve my skills
It doesnt improve my skills

>> Neither. This is a sentence fragment. What is "it"? If ,for example, "it" stands for a noun like; "It (Web surfing) is not improving my skills." or a descriptive phrase like "It (Talking too fast) does not my improve my skills."

Thanks for correction and answer haha

>> Thank you for the corrections and answers.