Short answer
In Western astrology, signs of the same element usually get on most easily, and fire pairs well with air, earth with water. Vedic astrology goes further and compares your Moon signs and birth stars (Nakshatras), using Ashta Koota matching scored out of 36 or Tamil Porutham with about 10 checks. A sign pairing is a starting point, never a verdict on one person.
How ChiChakra reads this
ChiChakra starts from your Moon sign. Ashta Koota scores eight factors out of 36 gunas; 18 or more is traditionally acceptable, with Nadi and Bhakoot (how many signs apart your Moon signs sit) carrying the most weight. Tamil Porutham looks at about 10 matches, where Rajju and Dina count most and about 6 or more is traditionally acceptable.
Using it well
Find both Moon signs and Nakshatras first; each person needs a birth date, time and place.
Treat a low score as a conversation starter: what do you each need when stressed, and how do you handle money, family and space? Treat a high score the same way, since it does not replace knowing each other.
Families who match charts also weigh the whole of both charts, including the 7th house and Venus, and how the couple actually get on. Mangal Dosha is very common and often cancelled, so it is no reason for fear.
Good to know
Respect, kindness and honesty matter more than any score, and no chart excuses someone treating you badly.