SEO plugin and custom meta description yes or no?

I am quite new to SEO and when i was researching some keywords i saw that most pages on the top do not use a custom meta description.
On my website i have the SEO by yoast plugin and I don't know if i should write my own custom meta descriptions and titles or not?

What is the difference between not writing any meta descriptions and writing them, I am confused if i should write them for my authority site or not?

I would rather write the meta description myself. It does help a bit in SEO by letting Search engines know what your site is about. It does makes a difference.