I think you are a

Typewriter

I have keys, but I don’t open any locks.

The typewriter has keys for typing letters

I got a ribbon but I didn’t win, place or show.

A typewriter has an ink ribbon for transferring pigment to paper

I need some help from nature to be useful

Pieces of paper, made from trees and usually called "leaves", so could be a play on words.

Part 2

It's usually said that typewriter the longest word which you can type only using the top row of letters.

Hint

"The quick brown fox jumped over the lazy dog" is a sentence that uses all the letters of the alphabet and can be used to check a typewriter is functioning correctly.

I think you are a

Typewriter

I have keys, but I don’t open any locks.

The typewriter has keys for typing letters

I got a ribbon but I didn’t win, place or show.

A typewriter has an ink ribbon for transferring pigment to paper

I need some help from nature to be useful

Pieces of paper, made from trees and usually called "leaves", so could be a play on words.

Part 2

It's usually said that typewriter the longest word which you can type only using the top row of letters.

Hint

"The quick brown fox jumps over the lazy dog" is a sentence that uses all the letters of the alphabet and can be used to check a typewriter is functioning correctly.