'create a new null",I don't know that what null is?I checked dict that null is about 'empty','0'.What is null's functionFor why to create a new null? Thanks.

A null is a node without any geometry - it can be useful for organising the scene without using much memory. For example, you can use a null as a target for things such as lights to point at, so that moving the null changes the direction of the light, or you can parent items to the null and just move or align the null to carry the parent items to a new position while keeping their relative placement.

Thanks cat.

I also use them to anchor people, both to get around problems with poses that move the character to 0 (since if they are hooked to a null that 0 is relative to the null, hence they don't move), or when trying to pose two or more characters in relation to each other - you can move the null without changing the relative positions of the characters to each other. Just be careful not to load too much on to the same null when you do that or it will slow your machine to a crawl, particularly if smoothing modifiers are active for clothing.

good  post