These advanced steps are primarily for system administrators and others who are familiar with the command line. You don't need a bootable installer to install macOS, but it can be useful when you want to install macOS on multiple computers without downloading the installer each time.

Download macOS

1. Attach your external hard drive to your computer via the USB cable and turn on the device. If you only want to create a single additional partition, click 'Next' to use the default, maximum.
2. To create a new partition, right-click unallocated or RAW space on the basic disk where you want to create the partition, and then click New Partition (Win XP) or New Simple Volume (Win Vista, 7 and 8). In the New Partition Wizard click Next 3.

1. Download a macOS installer, such as macOS Mojave or macOS High Sierra.
   To download macOS Mojave or High Sierra for this purpose, download from a Mac that is using macOS Sierra 10.12.5 or later, or El Capitan 10.11.6. Enterprise administrators, please download from Apple, not a locally hosted software-update server.
2. When the macOS installer opens, quit it without continuing installation.
3. Find the installer in your Applications folder as a single ”Install” file, such as Install macOS Mojave.

Use the 'createinstallmedia' command in Terminal

1. After downloading the installer, connect the USB flash drive or other volume you're using for the bootable installer. Make sure that it has at least 12GB of available storage and is formatted as Mac OS Extended.
2. Open Terminal, which is in the Utilities folder of your Applications folder.
3. Type or paste one of the following commands in Terminal. These assume that the installer is still in your Applications folder, and MyVolume is the name of the USB flash drive or other volume you're using. If it has a different name, replace MyVolume accordingly.
   Mojave:*
   
   High Sierra:*
   Sierra:
   El Capitan:
   
4. Press Return after typing the command.
5. When prompted, type your administrator password and press Return again. Terminal doesn't show any characters as you type your password.
6. When prompted, type Y to confirm that you want to erase the volume, then press Return. Terminal shows the progress as the bootable installer is created.
7. When Terminal says that it's done, the volume will have the same name as the installer you downloaded, such as Install macOS Mojave. You can now quit Terminal and eject the volume.

Right-click the existing partition on the external hard drive, select 'Delete Volume' and choose to remove the partition.

* If your Mac is using macOS Sierra or earlier, include the --applicationpath argument. The Sierra and El Capitan commands show the proper format of this argument.

How To Make Partition Usb For A Mac Using Mini Tool Partitioning

Use the bootable installer

After creating the bootable installer, follow these steps to use it.

1. Connect the bootable installer to a compatible Mac.
2. Use Startup Manager or Startup Disk preferences to select the bootable installer as the startup disk, then start up from it. Your Mac will start up to macOS Recovery.
   Learn about selecting a startup disk, including what to do if your Mac doesn't start up from it.
3. Choose your language, if prompted.
4. A bootable installer doesn't download macOS from the Internet, but it does require the Internet to get information specific to your Mac model, such as firmware updates. If you need to connect to a Wi-Fi network, use the Wi-Fi menu in the menu bar.
5. Select Install macOS (or Install OS X) from the Utilities window, then click Continue and follow the onscreen instructions.

Learn more

For more information about the createinstallmedia command and the arguments that you can use with it, make sure that the macOS installer is in your Applications folder, then enter this path in Terminal:

How To Make A Partition Usb For A Mac Using Mini Tool Partition

Mojave:

High Sierra:

Sierra:

El Capitan: