How do I create an installation boot disk?

1- Download required operating system such as ubuntu (Linux) from ubuntu.com

2- Open startup disk creator and select the downloaded ISO ubuntu file. 

3 - Insert USB/CD and locate it and slelect it.

4- Erase all data by clicking on Erase

5- Burn ISO file on USB/CD to create a startup disk.

6- After everything done use this USB/CD as a bootable device and continue for installation of LINUX system.

Brother I use Mac I use usbnetbootin avilable free of cost. If U happen to use Ubuntu it has a USB Disk Creator, but one issue a32 bit Ubuntu installation might not let U create a installation bootable drive for a64 bit architechture.  

Check out this article, it has all the tools you might need:

http://www.howtogeek.com/127377/the-best-free-tools-for-creating-a-bootable-windows-or-linux-usb-drive/

First you  have to confirm that iso which you are going to Burn is bootable or not...there are so many software for that.

then use any image burner for that process like nero, power ISO

for wich OS?