The prepositions à and de are found in many verbal constructions that look very similar, but the choice of preposition makes all the difference.
With regard to how they function in a sentence, verbs can be divided into three categories: action, state-of-being, and auxiliary.
Some French verbs do not allow their indirect objects to be replaced by pronouns; instead, the preposition must be maintained after the verb along with the indirect object.
The regular -er verb aimer is ubiquitous and very useful, but somehow means both "to like" and "to love." In some contexts, this can make a world of difference as you certainly don't want to tell someone you love them when you're just friends, so how can you make it clear how you feel?
Aller is one of the most common and useful French verbs and has irregular conjugations in most tenses and moods. Aller literally means "to go" and is used to create the near future.
The French verb arriver usually means "to arrive" or "to happen." It's a regular -er verb that requires être as its auxiliary verb in compound tenses/moods.
Avoir is one of the two most important French verbs and has irregular conjugations in just about every tense and mood. Avoir literally means "to have" but also serves an an auxiliary verb and is found in many idiomatic expressions.
Certain aspects of French grammar are a bit different with the causative than with other two-verb constructions.
Compound tenses and moods are verb forms which are conjugated with two parts: a helping / auxiliary verb and a past participle, as in J'ai dansé. The word order can get a little complicated when additional grammatical structures like object pronouns and negation are introduced.
Croire is one of the most common and useful French verbs and has irregular conjugations in most tenses and moods. Croire literally means "to believe," has somewhat varying meanings depending on the preposition used, and is found in many idiomatic expressions.