|They're called usb hubs; and come in two forms.|
One (effectively passive) is powered from the usb port. Generally does not provide enough power to charge devices, but certainly allow devices to work via that port.
Powered (effectively active) - has an external mains adapter - and will usually have one or more ports that can charge devices; will also allow usb devices to work of course via any of its ports.
The non external powered hubs are usually cheaper than those with external power...
I find many (no external power) hubs are adequate for my use. Although I do have a couple that do use external power as I have iDevices etc. that I can occasionally charge up with via port from those hubs.
If you enter "usb hubs" (no " ") into google - you will see what they look like; the different styles/models and the prices related to wherever you are.
I have found Amazon a decent source for both kinds; and occasionally my local PC/electronics stores too... Wise to shop around... Many of the hubs have a very short usb cable attached/built-in; invariably one requires an slightly longer cable... so one uses a decent extension cable.
Hubs come in usb-2 and usb-3 versions. The usb-3 is backwards compatible with usb-2 devices.