Conceptually, every step (like “WHERE”) of a query transforms its input, like this:

cats

owner: 1 name: daisy
owner: 1 name: dragonsnap
owner: 3 name: buttercup
owner: 4 name: rose

WHERE owner = 1

owner: 1 name: daisy
owner: 1 name: dragonsnap

The query’s steps don’t happen in the order they’re written: how the query’ is written SELECT…
FROM + JOIN
WHERE …
GROUP BY …
HAVING …
ORDER BY…
LIMIT…

how you should think about it:
FROM + JOIN ↓
WHERE
↓
GROUP BY
↓
HAVING
↓
SELECT
↓
ORDER BY
↓
LIMIT

(In reality query execution is much more complicated than this. There are a lot of optimizations.)