Concerning USB hubs, a 2.0 hub connected to a 3.0 port will still only provide 2.0?
You are correct. All USB hubs, ports, and devices are backwards compatible, which means they support the older versions as well as their current versions. So a USB 3.0 hub would work in a USB 2.0 port. However, devices will only function at the highest version supported by both devices. So if you have a USB 2.0 port and 3.0 flash drive, it will function at the 2.0 speed. Similarly, if you have a USB 3.0 port and a 2.0 device, again, it will function at the 2.0 speed.
As an additional note, if your computer only has USB 2.0 ports, the only way to upgrade them to USB 3.0 ports would be to install a USB 3.0 card on your motherboard. This does involve opening up the computer and inserting the card into an open slot on the motherboard. If you are not comfortable with working on the inside of a computer, this isn’t recommended. You would also need to do some research to verify that your motherboard will support USB 3.0, as older motherboards/computers may not.
Most times a USB 3.0 port is blue, so that is how you can tell if you have USB 3.0, though not always. But also keep in mind, a faster USB port will only typically be helpful when you are transferring file or data. So things like a mouse, keyboard, or any other USB device really won’t benefit if you upgrade. However, things like flash drives and external hard drives will show improved speeds.