I’ve had to do this to install both Windows and Ubuntu. Here’s how it goes:
Download the iso you need. Here are both Windows 10 ISO Download and Ubuntu 16.04 ISO Download. For others you can google them and find them quickly.
Once you have your iso downloaded to your ~/Downloads folder then you’re ready to make the disk.
Open spotlight by CMD + space for by clicking the magnifying glass in the top right corner of your screen. Type “terminal” into the Spotlight Search and press enter.
In the terminal screen type the following:
You’ll see something similar to the folowing screen. Get the number of the correct disk you are using. I am using a 64GB SD card so mine is safely the drive that is SIZE 63.9 GB which is /dev/disk2
diskUtil unmountDisk /dev/diskN
On this next line make sure you add the “R” before diskN, in my case I used “/dev/rdiskN”
sudo dd if=~/Downloads/name-of-your.iso of=/dev/rdiskN bs=1024m
if that doesn’t work then you can always try bs=1m. That’s telling your computer how fast to transfer the ISO to you removable media. 1m is slow but stable whereas 4096 is unstable and mostly like won’t work (it doesn’t work on my machine) so I recommend a modest number and 1024 is the highest that works on my 2015 mbp.