Google will take a snippet of description text from your webpage's content, but if it's well-written, they may use the meta description tags instead.
The meta description tag basically need to sum up what the page is about in a short sentence and ideally have a call to action at the end.
They can technically be any length but there is usually room for around 160 characters on the results page.
In the Google Search Central document covering ranking and snippets, Google says "They are like a pitch that convince the user that the page is exactly what they're looking for."
Our Budget SEO Package includes us working on improving the meta descriptions tags on your website. Find out more.