Venus, named after the Roman goddess of love, is one of the inner terrestrial planets. Venus' orbit is the second furthest from the Sun after Mercury and closer to Earth's orbit than any of the other planets.
Venus' has a thick atmosphere of mostly carbon dioxide with some sulpher dioxide, this means that Venus is completely covered with cloud at all times and virtually no detail can be seen with standard ground based telescopes. It also means Venus has a high albedo (it relfects light really well) so that when Venus is at it's closest to Earth in it's orbit it is the third brightest object in the sky after the Sun and Moon. If you know where to look it can even be seen in broad daylight!
From the Earth, the planet Venus goes through phases just like the Moon and for a similar reason. When Venus is at it's closest to Earth it is between the Sun and Earth so most of the light from the Sun falls on the side of Venus which we cannot see and we see a crescent. When Venus is furthest from the Earth more of it's disc is revealed as light from the Sun is falling on the side of Venus we can see. However, it is when it is in it's crescent phase that Venus is at it's brightest as that is when it is at it's closest to us.
Venus is best spotted after sunset or before sunrise depending on where it is in it's orbit.