UFS How can I move /usr to new disk?

How can I move /usr to new disk?

And second question, which paths must have large space I mean the standard?

Like the file of games where it will be installed and other apps?

Is it /usr or /var or what?
Depending on what you use it for but most of the time /usr/ will be the biggest. Keep in mind it contains things like /usr/ports, /usr/src/, /usr/local/ and /usr/home. All of which can grow quite large.
If / is not a large partition, additional kernels can take up a large portion of space too.

If you are new to unix, running du -h -d1 / will show you how much space each directory tree under / is using.