Sources: Things that give us information about past events. eg. Documents, Audio/Video, Artefacts (physical sources, eg: an ancient coin).
Primary Sources: Sources from the time of the event. eg. Eye-witness accounts, photos, speeches, diary entries, newspaper articles,etc.
Secondary Sources: Sources from a later date, often written or recorded by historians. eg. biographies, history texts, documentaries, movies, etc.
Evidence: Information taken from sources that historians use to back up their ideas about what happened in the past. Also known as 'the bits that you highlight on your source'.
Usefulness: The ways that sources and evidence are valuable in helping us to understand past events.
Limitations: No source is perfect! All have parts of the story missing. The missing parts are what we call the source's limitations.
Reliability: Whether or not we can trust what the source is saying. Most of the time this comes down to authorship - who wrote or recorded this and why?
Perspectives: Different points of view held by people about the same event.
Here's a great list of things to consider when thinking about sources in terms of their usefulness, limitations and reliability.
All in all, History is a bit like detective work...