Disk Utility complicated partition function

I've tried to create a 100MB partition an 1TB portable USB disk I have with El Capitan installed, but the partition function in the new Disk Utility of this OS is very complicated. I could not figure out how to create a this partition in order to install Bootcamp. I choose the size of the partition, and after completing the process, appeared 3 more Untitled partitions, and the main partition (the one with the OS) was only 40MB in size. I tried to fix the problem, and every time I tried Disk Utility created more Untitled partitions. I have to fix this drive and I cannot figure out how. I don't know why Apple modifies an utility and transform a simple task (I have used this function several times in the old Disk Utility) in a nightmare like that.

Someone can help me?