Bonjour
An independent clause includes a subject, a verb and expresses a complete thought (une proposition indépendante).
As its name implies, it stands alone.
A main clause (proposition principale) could stand alone but it's followed by a relative pronoun or a subordinating conjunction attaching it to a subordinate clause (proposition subordonnée)
A subordinate clause is attached to the main clause.
exemples=>
he likes the cake ---> main clause
he likes the cake that you cooked -- > main clause + subordinate clause
hope this will help :)
