Open Graph (OG) is a set of meta tags that tell Facebook, LinkedIn, Discord, WhatsApp and other platforms how to display your link when someone shares it. Without them, the preview picks random text and often no image.
1200 x 630 pixels is the Facebook and LinkedIn standard. It also works for Discord, Slack and Signal. Under 300 x 200, some platforms won't show an image at all.
Twitter uses Open Graph as a fallback, so you don't strictly need Twitter-specific tags. But adding twitter:card and twitter:image gives you tighter control over the Twitter/X preview.