The USB port on the Roku is for power so you don't need to connect it to the TV. You just need a power supply with a USB connector that should have come with the Roku.
I'm sorry i'm 65 and a newby and I don't know what a thread is.What is a thread??
You can use an HDMI switcher splitter, like this one from Amazon. Plug the single end into your TV, the other devices into the end with the 3 HDMI ports, and it automatically switches to the correct port depending on which device you turn on. I've used it for years without any problems when I had an older single HDMI port TV. I'm assuming your Roku box has a USB port on it, it will work through the Roku.
The USB port on the Roku is for power so you don't need to connect it to the TV. You just need a power supply with a USB connector that should have come with the Roku.