virsh and virt-install are good tools for individuals who are getting started with VMs on Linux. It sounds a bit old hat now, but if you can do something well on the command line, you'll wonder why you ever needed a clicky-button GUI to do the job for you.
When we talk about clients in this way, what we're referring to are frontends to the libvirt library, which is a C toolkit that was designed to make interacting with the kernel's virtualization functionality easier.
virsh and virt-install talk to libvirt, which, in turn, talks to the kernel.
