There is no retrograde motion of Venus and Mars, in 2019. The other planets will be retrograde, one or more times (this is the case for Mercury and Uranus), during this year.
Retrograde motion of a planet is its apparent backward motion through the sky, as observed from Earth. This apparent retrograde motion is caused by the Earth traveling past a slower-moving outer planet (Jupiter, Saturn, Uranus, Neptune and Pluto) or when the Earth is itself passed by a faster-moving inner planet (Mercury, Venus or Mars).
So, this is like the apparent motion of the slower car on the highway – an optical illusion. But it is important, from our perspective: we live on Earth and we judge things from an earthly perspective.
Some astrologers consider this apparent backward movement of the planets was to be unlucky, because it goes against the natural order of movement – the direct movement. But a retrograde planet is not necessarily something bad – actually, it is a chance to recognize, understand and correct past mistakes.
Retrograde Planets in 2019
March 5th-March 26th: Mercury retrograde in Pisces
July 9th-July 31st: Mercury retrograde in Leo and Cancer
November 1st-November 18th: Mercury retrograde in Scorpio
April 10th-August 11th: Jupiter retrograde in Sagittarius
April 30th-September 18th: Saturn retrograde in Capricorn
August, 7th, 2018-January 6th, 2019: Uranus retrograde in Taurus and Aries
August 12th, 2019-January 1st, 2020 Uranus retrograde in Taurus
June 21st-November 27th: Neptune retrograde in Pisces
April 24th-October 3rd: Pluto retrograde in Capricorn