USB installers mostly are needed to downgrade the macOS version or to make a clean install of a macOS.

Before starting the procedure, make sure you have an installer you need (if needed, download here).

OS X 10.11 or later

To make a bootable installer for OS X El Capitan 10.11 or later, you need to open up Terminal (Launchpad > Utilities > Terminal.app), plug in your USB stick, rename it as MyVolume and hit enter.

Now, enter the following Terminal prompts for your system:

macOS 13 Ventura:

sudo /Applications/Install\ macOS\ Ventura.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume

macOS 12 Monterey:

sudo /Applications/Install\ macOS\ Monterey.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume

macOS 11 Big Sur:

sudo /Applications/Install\ macOS\ Big\ Sur.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume

macOS 10.15 Catalina:

sudo /Applications/Install\ macOS\ Catalina.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume

macOS 10.14 Mojave:

sudo /Applications/Install\ macOS\ Mojave.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume

macOS 10.13 High Sierra

sudo /Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume

macOS 10.12 Sierra

sudo /Applications/Install\ macOS\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ macOS\ Sierra.app

OS X 10.11 El Capitan

sudo /Applications/Install\ OS\ X\ El\ Capitan.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ OS\ X\ El\ Capitan.app

As you may see closely, the codes for macOS 10.12 and OS X 10.11 also feature the
--applicationpath prompt, so keep an eye on that.

Mac OS X 10.7 - OS X 10.9

In OS X 10.11 or later

To make a USB bootable installer, you need to open Disk Utility (Launchpad > Utilities > Disk Utility) and do following steps:

1) Plug in your USB stick, hit Cmd+2 in Disk Utility and select the USB stick device in the sidebar.

2) Click "Erase". In dropdown window, select Mac OS Extended in Filesystem, GUID Partition Table in Partitioning and click Erase.

3) After erasing, open the folder with installer, click on the installer and hold the Ctrl button and click "Show package contents".

4) Go by following direction: Contents > SharedSupport.

5) Now, get back to Disk Utility and click Restore. Drag the InstallESD.dmg to the Restore from... dropdown menu and hit Enter.

6) If you see the green dingbat tick on the progress window, you have completed the process and you are ready to go!

7) If you see the error message, hit Close, hit Cmd+2, select your USB in the sidebar and do the same process again.

In Mac OS X 10.7 - OS X 10.11

To make a USB bootable installer, you need to open Disk Utility (Launchpad > Utilities > Disk Utility) and do following steps:

1) Plug in your USB stick and select the USB stick device in the sidebar.

2) Click "Erase". Select Mac OS Extended in Filesystem, GUID Partition Table in Partitioning and click Erase.

3) After erasing, open the folder with installer, click on the installer and hold the Ctrl button and click "Show package contents".

4) Go by following direction: Contents > SharedSupport.

5) Now, click on Restore tab and drag the InstallESD.dmg file to Restore from... dropdown menu.

6) If the progress bar in the bottom right corner has disappeared with no error messages, your process is complete and you are ready for installation.