The accusative case is a noun or noun equivalent that functions as the direct object of a verb in a sentence.

I told it = IT is in accusative case.

I don't know them pretty well. = THEM is in accusative case.

I took my sister to the hospital for an examination = sister is in accusative case.

Remember, In English in contrast to other languges such as german or spanish, just the pronouns suffer changes in their form, the rest of the noun or noun equivalents stay the same without any alteration in their form.