Your origin is where your character comes from, and it is two choices rather than one: a species, which is what you are, and a background, which is what you did before the adventure started.
They divide the work cleanly, and not the way older editions divided it.
A species carries your creature type — almost always Humanoid — your size, your walking Speed, and a short list of traits. Those traits are the interesting part: senses like Darkvision, a resistance, a small innate spell, a way to move that other characters do not have.
A species grants no ability score increases. Not one. If you are choosing a species to make a number bigger, you are reading a version of the game that is two editions old — pick the one you want to play.
Some species also offer a lineage: a named variety within the species that swaps in its own traits. Where one exists it is a second, narrower choice made at the same time, and the species page lists what is available.
Your background is where the mechanical weight of your origin sits. It carries:
That makes the background the mechanically louder half of your origin, which is worth knowing before you choose one to match a backstory you have already written. The two do not have to agree — a background is a summary of a life, not a contract about it — but the abilities it raises should point at the class you picked.
Species and background are independent: any species can have any background, and nothing in the rules pairs them. What is worth sequencing is the background against the class, because the background's ability increases are the difference between a good primary ability and a great one — see ability scores.