For the price you get a nice large cloth that can be used to clean rosin, sweat etc. off the instrument and strings. Because it is a microfibre fabric you won't get bits of fluff attached to the string or elsewhere, and it's more effective at cleaning stuff off the varnished front of a string instrument.
I have no doubt this would also be excellent for cleaning more than just string instruments; so I bought an extra one to clean my brass instruments with.
There are no washing instructions unlike the (much more expensive, and tiny) microfibre cloth I bought recently from a local shop. But I am sure these cloths are washable and should be kept clean regularly in order for them to work properly..