Partitions and RAIDS
If you know what RAIDs and partitions are, the first question you are probably asking is why you would ever want or need to combine them. My answer would be that you might want a partition larger than one of your hard drives.
Lets say that you have two 100GB hard drives and you would like to separate your operating system(OS) from your files and applications.
You could leave your two hard drives as is. That would mean 100GB for your operating system only, and 100GB for everything else. I don't think there are many operating systems that require even close to 100GBs, so it would be much more efficient to give the extra space from your OS drive to the files drive. To do this, you would need to use a combination of RAIDing and partitioning.
The order of operations you use when combining RAIDS and partitions is quite important. You can't partition are RAID, but you can RAID partitions. That means that in this case you would have to split the first drive into two partitionslets say 25GB for the OS and 75GB for the files. Then you would RAID the 75GB partition with the entire second hard drive. That would leave you with a 25GB OS partition and a 175GB files partition.
I will note that this technique only works with JBOD or Concatenated RAIDs which aren't truly RAIDS given the fact that there is no redundancy. However, for all intensive purposes you are still creating a RIAD.