The main ubuntu installer is quite accessible, I installed ubuntu that way, on a secundary harddrive. If you want to start orca to make it accessible, once you hear the sound, press alt+super+s.

Download rufus.ie and make a USB with it. Maybe you have to make gPT, or MBR USB. I dunno, but you'll have to figure that out. Most machines will boot to the USB through a menu if you press f12, or something like that. You may have to research for your PC. Depending on the distro you may be able to boot without bios modification, but depending on your PC you may have to do those changes people talk about.

well, exactly as other people mentioned above, write the image to a USB media, insert it into the computer, turn it on...
At this point, however, I am afraid that you must, if you aren't lucky enough that it's set as such by default, mess abit with the bios. Note: it would be best if you could get sighted assistance at this point, as to not make it a very unplessent experience for both your computer, ocr device and usb thing. Luckily, you need to do this only once per computer, so no big deal there.
Let's suppose we got past that offleness with the bios for now, so, we just go on...
all you have to do right now is to wait untill the computer boots in the installer. It may pass afew seconds or even a minute untill it does. If you waited for longer than a minute and still nothing, get your phone or whatever you're able to do ocr with, because you'll need it as a problem just happened and you are in the bios, remember, so no screen reader. When it finally does boot, you'll hear a sound much like a drum. Then, press alt+windows+s to start orca.
the instalation will be pretty standard by now, but if you have any questions, feel free to ask.