There are 4 types of relationship between planets: -
Combination Relation: -When two or more than two planets are present in the same house of the chart then combination relation or 'Yog Sambandh' or 'Yuti Sambandh' is said to be taken place betweem them. Just like in the chart given below Sun, Mars, Mercury, Jupiter & Venus are present together in the 10th house.
Unidirectional Vision Relation: -When one planet is observing some other planet but that other planet is unable to watch the first one. Just like in the chart given below Jupiter is observing Mercury with its 5th vision but Mercury is unable to watch Jupiter.
Bidirectional Vision Relation: -When two planets are watching each other simultaneously. Just like in the chart given below Mars is watching Saturn with its 4th vision & Saturn is also watching Mars with its 10th vision. Similarly Jupiter & Venus are watching each other with there 7th visions.
Exchange of Zodiacs Relation: -When two planets exhange their zodiac signs which means the first planet is present in the zodiac of the second planet whereas the second planet is present in the zodiac of the first one. Just like in the chart given below Jupiter is present in the sign of Scorpio (which is the sign of Mars actually) whereas Mars is present in the sign of Pisces(which is the sign of Jupiter in actual). This way both Jupiter & Mars have exchanged houses. Similarly Moon & Saturn have also exchanged houses and Sun & Mercury have also exchanged houses.