Suited connectors
Suited connectors are two hole cards of the same suit that sit next to each other in rank, like the 8 and 9 of hearts, giving straight and flush potential.
Suited connectors are two hole cards that are next to each other in rank and share the same suit, such as the 8 and 9 of hearts. Because they're connected, they can make straights, and because they share a suit, they can make flushes, which gives them more ways to grow into a strong hand after the flop than a random pair of cards.
They come up most when you're deciding whether to play a hand before the flop, especially from later positions like the cutoff or the button. On their own these cards rarely win at showdown unimproved, so the appeal is the potential: when they hit, they often hit big and can win a lot of chips from someone holding a high pair. When they miss, they're easy to let go of with a fold.
As a beginner, treat suited connectors as a hand you play cheaply and in position rather than a hand to commit a lot of chips with early. If the flop brings you a real draw, like an open-ended straight or a flush draw, you have plenty of outs and can keep going; if it brings you nothing, folding is usually fine. Avoid calling big raises with them just because they look fun, since most of their value comes when you can see a flop without spending much.
Example
You're on the button with the 7 and 8 of clubs and call a small raise. The flop comes 6 of clubs, 9 of hearts, and 2 of clubs, giving you an open-ended straight draw plus a flush draw, a great spot to keep playing.