Who is whom?

The confusion between who and whom often occurs in my students' written assignments. Hence I will deal with their difference in this post, hoping to be of help to other leaners of the English language.

The relative pronoun 'who' refers to the subject in front of it. These are some examples of how to use 'who' as a relative pronoun.
a) She is the girl who often helps me when I am in difficulty. ['who' here refers to 'the girl', the subject in front of it.]

b) Those who win who get their prizes in cash. ['who' in this sentence refers to 'those', the subject in front of it.]

c) The man who cheated my neighbour is still in town. ['who' in this case refers to 'The man', the subject in front of it.]

As for the relative pronoun 'whom', it is just the objective case of 'who'. In other words, it refers to the object instead of the subject. Let us look at a few examples to see how 'whom' is correctly used.
a) He was the man to whom I gave my application letter. ['whom' here refers to the object 'the man'. The sentence comes from two sentences, that is, 'He was the man.' and 'I gave my application to the man.']

b) She was the girl with whom I travelled from Perlis to Johor Bahru. ['whom' here refers to the object 'the girl'. Here again, the sentence comes from two sentences, that is, 'She wsa the girl.' and 'I travelled with the girl from Perlis to Johor Bahru.']

c) He was the officer from whom I obtained this information. ['whom' here refers to the object 'the officer'. The two sentences that are combined to form the above sentence are 'He was the officer.' and 'I obtained this information from the officer.]

So much for the different usage of 'who' and 'whom'