First, the meaning is different.
assure
Confirm; Set ... comfort
ensure
Guarantee; Guarantee; Make safe; ensure
Second, the usage is different.
assure
Assure is a transitive verb and can take a noun or pronoun (not a clause) as a simple object.
Assure can take double objects, in which case the object of the object must be led out by the preposition of; If you put the table object after it, you must use the preposition to (not for). If you put it before it, you don't have to match the preposition.
When assure is followed by the object of the object, it can act as that clause or infinitive.
The news reassured mother.
The news reassured mother.
ensure
The basic meaning of guarantee is that someone makes an oral or written promise to others, emphasizing that people will believe that the consequences of a certain behavior or force will, will and will definitely appear.
Make sure that it can be used as both a transitive verb and an intransitive verb. When used as transitive verbs, nouns and that clauses can be used as objects, and that clauses can be used in declarative mood or subjunctive mood. Ensure can also be followed by a double object, and its indirect object can be converted into the object of the preposition for. When used as an intransitive verb, it can be followed by the preposition from, which means "protect someone from harm"
If you want to make sure you catch the plane, take a taxi.
If you want to make sure that you can catch that plane, take a taxi.
Third, the emphasis is different.
assure
It means "guarantee", and assure usually means to dispel someone's doubts or worries.
ensure
It means "guarantee", ensuring that emphasis is placed on convincing people of the consequences of an action or force.