The USB standard defines the way in which a device talks to the host. Unless you're taking advantage of a brand new standard called "USB On the Go" (USB-OTG) which allows devices limited host capabilities, you're probably going to be connecting a device directly to a host.
99% of host controllers will have a USB-A receptacle, so when you're looking for a USB cable, you'll usually be looking for a "USB A-to-something" cable. A lot of the time the USB-A end is assumed, since that's the connector on most PCs, and cables will be named after the connector on the opposite end. Some smaller hosts use a Mini or Micro receptacle but they usually supply a pigtail adapter to USB-A.