1. "Roger" means "understood" and "Wilco" means "I will comply" but both are unnecessary, because just reading back your callsign means "received, understood, and will comply" all in one.

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2. "Roger" means "understood" and "Wilco" means "I will comply" but both are unnecessary, because just reading back your callsign means "received, understood, and will comply" all in one.

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3. Some old pilots do this. DON'T. It's useless and annoying, and you'll still be asked to read back an acknowledgement.

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4. A transmission containing nothing but the call sign means, "I have received your transmission, I understand it, and I will comply" If there is anything you do not understand or do not agree with, you must say so. "Victor Whiskey X-ray unable runway 26. I am on floats" "Alfa Bravo Charlie unable runway one nine. I require at least 2000 feet to land." "This is Uniform Charlie Kilo, I do not understand the clearance." It's WAY WAY better to say "Echo Delta Foxtrot is a student pilot. Say again slowly" than to get run over by a 737.