grape
The French word 'raisin' is used to refer to a grape — a small, round, purple or green fruit that grows in clusters on vines, it is the same usage as in English. Note that in French, 'grape' is a false friend with the English 'raisin', which is actually a dried grape; the French refer to this as 'raisin sec'.
I like to eat grapes.
This sentence is an example of expressing a specific food preference in French. The indefinite article 'du' is used before the noun 'raisin' (grape) which shows affection towards the food.
The grape is ripe and sweet.
This sentence describes two qualities of the grape. The use of the conjunction 'et' (and) allows you to combine multiple adjectives in one sentence. Note the position of the adjectives after the noun, which is usual in French.
He sells grapes at the market.
This sentence demonstrates how you would express the act of selling something at some place in French. The preposition 'au' is a contraction of 'à le', which translates as 'at the' in English.