In a physical game, make your intention clear; in online chess, use the platform’s resign control. A handshake or other gesture can be ambiguous, so do not rely on an unclear signal when the result matters.
Beginners often benefit from playing difficult positions out: the opponent may miss a tactic, and defending teaches useful skills. There is no obligation to resign merely because you are behind in material.
When you choose to concede, review one critical moment afterward. Identify the threat or decision you missed and turn it into a concrete practice question.