grass
The French word for grass is 'herbe'. It is used in the same way as in English, to refer to the green plant that grows on the ground. For example, 'Il y a de l'herbe sur le terrain' means 'There is grass on the field'.
The cat is on the grass.
This sentence describes a simple scene where a cat is located on the grass, using the preposition 'sur' to express 'on'.
The grass is green here.
This sentence is expressing an observation about the grass being green in a specific location, which is here.
Do not walk on the grass.
In this sentence, an imperative form 'Ne marche pas' is used to give an order or instruction not to walk on the grass.