What is a subject and a predicate in a sentence, and how do I tell them apart?

Every complete sentence has two main parts. The subject is who or what the sentence is about, and the predicate tells what the subject does or is. To find the subject, ask 'who or what?' before the verb. Everything else, including the verb, forms the predicate. For example, in 'The little boy ran to school', ask 'who ran?' The answer is 'The little boy', which is the subject. The rest, 'ran to school', is the predicate because it tells what the boy did. Another example: in 'My sister is a doctor', the subject is 'My sister' and the predicate is 'is a doctor'. The subject usually comes first, and the predicate always contains the verb. Practising with the 'who or what' question makes it easy.