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For the scent of a rose, it would be "A pleasant aroma", for the fresh grasses it would be, "The smell of freshly cut grasses". The good ones I would say, are used to describe good smells. Examples of "good ones" are - The beautiful fragrance of the flowers. The strong aroma of his perfume. I believe there are some more, which I can't remember but perfume is not a smell it's a box ( kind of ) which contains good smells.
Hope this helps !

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Yeah it's definitely a complex topic.

The most common way people describe new smells is by comparing it to something they already know. You could describe American barbeque as smelling "smoky."

Here's a pretty good article on lots of words about smells: https://www.writerswrite.co.za/75-words-that-describe-smells/

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Roses and grass can be pretty tricky! The smell of roses and grass (and a handful of other items) are distinct, and it's kind of expected that everyone already knows what they smell like, in fact, sometimes they are even used to describe other smells, (eg. "The room smelled of fresh grass").

You can try using adjectives to highlight a certain aspect of the smell, for example:
"The grass smelled clean and refreshing"
"The smell of the rose was strong and intoxicating"

You can also try using metaphors and similes, for example:
"The grass smelled as refreshing as a waterfall"
"The smell of the rose was heavenly"

As for the difference between perfume, fragrance, scent, and aroma, they are more or less used interchangeably with slightly different connotations.
Perfume usually refers to the thing that women wear that you buy at cosmetics stores
Fragrance usually refers good and/or sweet smells
Scent is a pretty neutral term that can be used for basically any smell
Aroma usually refers to good smells, often used with good smelling food

And yes, incense is typically for smokey smells. Though I think this word is more common as a noun, which is used to refer to the thing that you burn at temples.

Let me know if you need anything clarified! I can explain in Chinese too.

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Ohhh boy, here we go. I'm gonna try and explain this to the best of my abilities, and if you're confused at all, just reply.

For Bad smells:
For general bad smells, we would use the words "putrid" "stinky" "smelly" or "nasty." If you want to get more expressive or detailed, you'd use a negative adjective (For example, horrendous) and combine it with the word "smell" or "odour" (though smell is more common.) Otherwise, we'd use similes, such as "it smells like rotten eggs" or "it smells like actual poop." There are more vulgar expressions, but you'll find those the more English media you read/watch.

For good smells:
This is where we would use enticing words, such as "Fragrance" "aroma" or "scent." When describing good smells, you'd use you a positive adjective (sweet, for example) and combine it with either of the 3 words I mentioned before hand. For things like wood burning, you'd use "smoky," since that is what's produced when wood is burnt. Roses are a bit of a weird one, as the smell is quite distinct. So in that case, you'd say something like "the alluring scent of roses."

I once again apologise for my shoddy way of explaining it. Smells are a bit of a weird thing, and some of them can be indescribable.