There's a fine line between (something) and (something)

When two things are very similar, and it's hard to clearly define the difference between them, you can use this phrase:

There's a fine line between drinking socially and alcoholism.

There's a fine line between helping your kids with their homework and doing it for them.

There's a fine line between dressing a little sexy and looking trashy.

Usually, one of the things is good or OK, and the other one is bad. The bad one comes last.

help (someone) with (something)

You can use this phrase to describe helping someone to do a certain activity.

I help my grandma with her garden.

He needs someone to help him with all these reports.

Notice that "garden" and "all these reports" are both noun phrases.