I wouldn’t call this plagiarism as these suggestions are freely available, I’d call it research…
There are people with a great eye, and others who have studied graphic design. They suggest font pairings, and I’m happy to learn from them.
I’ve been collecting some great ideas for font pairing on Pinterest if you’d like to look. You can use Canva for free to make your images and you’ll find most of the fonts there.
Disclosure: This is a system that pays commission, so if you join, I’ll receive commission.
For a web design, your theme will have default fonts. If you want to change them, be careful if you aren’t comfortable with coding.You can access Google fonts from your dashboard.
To change a font, you edit the style.css stylesheet in WordPress through Appearance > Editor. It’s not a task for anyone who doesn’t understand coding though.
Otherwise, you could look around for other themes with the fonts you want, or you could make graphics with a program like Canva and upload them. There will be other fonts on your site, but it depends on how you have designed the site.