New players check the radar to see where their dot is. Pros check the radar 4-5 times per round to see where teammates have died, where utility is detonating, and which sites need defenders.
When a teammate dies, the dot turns into a skull icon. Two skulls in 5 seconds at the same site means execute incoming — you should be on rotation.
Smoke / molly icons appear on the radar. A smoke at A jungle on Mirage means T-side is doing the standard A take — start rotating from B.
Default radar zoom is too tight. Set cl_radar_scale 0.5 or 0.4 to see more of the map. Trade off: enemy positions show smaller, but you see all 4 teammates at once.