A transitive verb needs an object to complete the meaning of the sentence. An intransitive verb does not require an object to make its meaning clear.

The Transitive verb
A transitive verb must have an object. Without an object, it does not convey a clear meaning.
Example: He bought.

The question inevitably arises: "What did he buy?" No one knows the answer to this question as there is no direct object to receive the action of the verb 'bought'. The meaning becomes clear when an object is added as follows:
Example: He bought a cake.

The subject of the verb 'He' performs the action: bought. The object of the action verb 'bought' is a ' cake'
A transitive verb may take an indirect object. An indirect object is something or someone for whom the action is carried out.
Example: He bought her a cake.

The indirect object is 'her' as it's for her that the cake was bought. The indirect object usually precedes the direct object.

The Intransitive verb
An intransitive verb does not require an object. Without an object, its meaning is not affected.
Example: She swims.

The intransitive verb 'swims' does not need an object to make the meaning clear.
Example: The villagers caught a boar yesterday but it escaped this morning.

The verb 'caught' is transitive as it has the direct object: boar; the other verb 'escaped' is intransitive since it is not followed by an object.