A Meta pixel is a tracking tool that lets Meta (Facebook/Instagram) know what happens after someone clicks your ad. You set it up once in Meta's Events Manager, grab the Pixel ID, and add it to your SubmitHub Link. From then on, every visit and click on your Link gets reported back to Meta so it can optimize your ads.
Why bother?
You don't technically need a pixel to run ads, but without one you're flying blind. Meta can't optimize delivery (finding more people like the ones who actually clicked your Link), you can't set up conversion campaigns that chase specific actions, and you won't see detailed performance breakdowns in Ads Manager. If you're spending real money on ads, a pixel pays for itself.
Getting one
Head to Meta's Events Manager and follow their walkthrough to create a new pixel. You'll get a Pixel ID (a long number). That's what you'll paste into your Link.