question

if there's two pair on the board and someone is holding a lower pocket pair then on the board and the other player has high card what plays?

Best 5 card hand wins. So if you hold 44 and you opponent hold A2 and the board is 6677J, you lose (you play the board and he plays 2 pr A kicker). If you hold 44 and he has 910 with the same board it's a split pot (both have 2pr J kicker).