There are 5 main elements Earth,Fire,Lightning,Water,Wind these make up some of the basic Justus in the ninja world and each element has there own advantages and also each have there own disadvantages forming a circle of weakness and advantages.Since the time it takes to master and learn an element takes so long it is not possible to learn all the elements through natural methods but some like the rinnegan allows the user to have all 5 elements and others.The elements aren't limited to just the five elements some have a kekai genkai that allows one to mix two different elements and make a new element an example is in the senju there is a low chance that they could get wood release and to learn your element you put have a chakra paper that absorbs the chakra and changes to the result of the chakra that is your main element.