The car crashed into a tree
In a given sentence , there are mainly three things included , a subject , a verb and a object.
A subject is a noun . The subject is the actor of the sentence, the person or thing doing the action. The car in the above sentence represent a name of a thing therefore it can be classified as a noun.
Then in the middle of the sentence comes the verb which represents an action . The verb is the 'doing word', the action of the sentence. The word crashed is a action word . Hence it is a verb.
At last comes the object which represents the element of the sentence that is acted on, that the verb is directed towards. It can be seen clearly from the above sentence that the object is the tree as the verb crashed is directed towards it.