The vast majority of western astrologers use the Tropical zodiac. Our charts are based on the seasons, not on the stars. These two zodiacs are two perspectives for analyzing the sky. Both are valid and consistent within themselves. Each provides information in its own way.
All planets appear to move retrograde, or backwards, from time to time.
Mercury turns retrograde three times a year for about 21-24 days at a time. Since it's the planet of communication and details some people seem to have more difficulty in these areas when Mercury is retrograde. Some astrologers counsel against signing documents or making major decisions during these cycles. I don't think this is practical or necessarily true. When any planet is retrograde it is passing over territory where it has just been seen.