Here’s a useful, scenario-driven story to help you understand for MCPE 1.21.0 — including how to download and install it safely. Title: The Lag-Free Adventure of Alex and the 180k Pack

One evening, his friend Jamie whispered, “Try Flamefrags 180k. It’s small, fast, and works on 1.21.0.”

He joined a crowded server. Fire didn’t block his view, water was see-through, and his FPS jumped from 20 to 45. “Wow,” he laughed, “180 kilobytes did all this?”

He tapped the .mcpack file. MCPE opened and said: “Importing…” Then he went to Settings → Storage → Resource Packs and activated “Flamefrags 180k” for his world.