When it is not specified what the helper did...
私はとても忙しいので、彼を手伝うことができない。
When both action and person being helped are specified...
彼女は私に仕事を手伝うように頼んだ。
When it is not specified whom the helper helped...
彼はこの計画を手伝うだろう。
Is there some patterns or It's just that I don't understand? And if I want to say... "Can you help me clean the classroom?" with くれる, 手伝う, and 掃除, what will the sentence be like?
The meaning of 手伝う is: 《五他》他人の仕事をたすけて、うまく行くように力を添える。 "To help with people's work, pay effort to make sure it works out well."
So you can understand it this way:
私はとても忙しいので、彼を手伝うことができない。
As I am really busy, i cannot help him ( with his work ).
彼女は私に仕事を手伝うように頼んだ。
She asked me to help with her work.
彼はこの計画を手伝うだろう。
He will probably help with the project.
As Japanese is a Topic-Prominent Language, the informations that are irrelevant or commonly known by both the speaker / reader are usually omitted.
So to say "Can you help me clean the classroom?" with くれる, 手伝う, and 掃除, there will be two ways:
Which those information within the bracket can be optionally omitted, if you feel like it.
Hope that helps.
