How to break a Tie for a 3-of-a-kind
When figuring out who wins in Texas Holdem you take the best 5 card hand a player can make using their 2 cards plus the 5 community cards on the table. That gives us:

Player 1: 10, 10, 10, K, 6
Player 2: 10, 10, 10, K, 4

Since they both match on the 3 tens you look to the highest kicker card, in this case they both have kings so you need to look at the next highest card. For this card Player 1 has a 6 and Player 2 has a 4 so Player 1 will win the hand.

Reference: Texas Holdem Rules