"Paragraphs are made up of propositions. These are statements, questions, acclamations. They have a verb, they have a subject, and then other things surrounding those. That's a proposition." (John Piper)
So for example, the sentence "I am not ashamed of the gospel, for it is the power of God unto salvation for all who believe" in Romans 1:16 has two propositions: I am not ashamed of the gospel and for it is the power of God unto salvation for all who believe.
Other examples.
To help you split-up propositions on your own, let us take a few moments to refresh on grammar.