Water parameters are the measurable qualities of your aquarium water — temperature, ammonia, nitrite, nitrate, pH, GH and KH — that together tell you whether the environment is safe.
"Get the water right" is really shorthand for "keep the parameters in a stable, safe range for your fish." A liquid test kit is far more accurate than test strips and is the single most useful thing a beginner can own.
Test, don't guess: clear water can still be dangerous, and cloudy water can be harmless — only the numbers tell you which.