exercise
The French word 'exercice' is used to refer to a physical or mental activity done to maintain or improve one's health or skills. It is a direct translation of the English word 'exercise' and is used in a similar context, such as 'I do exercise every morning.' or 'This is a good exercise for learning French.'.
I do exercise every day.
This sentence is expressing a habitual action in the present, which in French is done by using the present tense. The verb 'faire' (to do/make) precedes 'de l'exercice' (exercise). In general, when an undefined amount of a noun is being used, 'de' is used before it.
Exercise is good for health.
In this sentence, 'L'exercice' (The exercise) is the subject of the sentence. It uses 'est' which is the verb 'être' (to be) in third person singular, and 'bon pour la santé' (good for health) is the predicate.
This exercise is difficult.
Here, the demonstrative adjective 'Cet' (This) is used before 'exercice' (exercise) to point out a specific exercise. The sentence is expressing a state by using 'est' (is) which is the third person singular of the verb 'être' (to be), and 'difficile' (difficult) as the adjective.