The meta title is the page title shown in search results and on the browser tab; the meta description is the short snippet displayed beneath it. The title is a ranking factor; the description mainly determines whether people click.
Good craft: a meta title up to about 60 characters, with the main phrase near the beginning and the brand at the end; a meta description up to about 155 characters, answering the intent with one specific detail and a reason to click. Google can rewrite both when it finds them off-topic – but carefully written ones get rewritten less often.
An example from this site: "Custom website design and development – design and code in one team | Sweet Lava". Phrase, promise, brand: all in one sentence you can read aloud.
Why it matters for business: the meta title and description are your advert in the search results – the only fragment of the page everyone sees, including those who never click. A ranking without clicks brings no customers; polishing the metas can lift traffic without moving a single position.