A bookmark is a link to a website saved for later reference in your web browser or computer. Saving a site address or sharing it on social media (example: pouyaeti.com) let users share websites they like with each other. Having links to your site in sites is a sign to crawlers that your website content is interesting to people.
What is social bookmarking?
This strategy saves information online, not on your device. That means you can access it anytime and anywhere with an internet connection.
Also when you are building a web page, you can define what image to show when it is shared on social media platforms. Specially for WordPress, there are some specific plugins that will help you define different images with different sizes for social media platforms.