Kekkei genkai/bloodline limit(naruto)?

how do the kekkei genkai that allow you to combine elements work?the mizukage had 3 elements and she was able to use them to make lava and mist styles.do kekkei genkai allow you to combine any elements that you have to make a new one or is it just certain ones(like if yamato were to get a fire element,would he be able to use mist or lava or would he still only be able to use wood?)?can you alter the amount of chakra to change the element(earth+water=wood,water+earth=pla… it possible to combine more than two elements?