I am really new to Ubuntu/Linux, and I am trying to make a bootable USB drive so I can freely change between OSs on my laptop until I am more comfortable with Ubuntu. I went to he Ubuntu website and followed the instruction for making a bootable USB device. So at this point I have Ubuntu installed on my USB but I do not know how to actually boot my computer to the OS.
Some older models don't support USB boot at all. This might be the case for your laptop, if it's old. You can check by entering the BIOS Setup (not the BIOS boot menu), and looking at the boot order. If there's nothing there for USB or "external drive" (or similar), it probably does not support booting from USB devices.
A common issue that I have faced (when installing Ubuntu on Portable Hard drives) is that the hard drive does not get detected when the system is booting up. This is possibly because of the lag in reading the physical drive extension and can be rectified by pressing Ctrl+Alt+Del before the windows boot screen comes. This will trigger another restart to the system and end up identifying the hard drive boot loader faster.
In this case, simply changing the boot priority sequence by going to the BIOS (have a look at the first screen of the computer startup, even before the windows screen - there would be an options list for eg:
- Del for setup or
- F9 for setup etc.)