Step 2) After you have logged in to your account successfully, click on the Mail icon.

Step 3) Now, you will be in the inbox, click on the Settings icon located at the left-bottom corner of the screen that looks like a gear cog, select the Preferences option from the sub-menu.

Step 4) A prompt will appear in the middle of the Window; by default, it will be on the General tab. However, go to the Account tab and there click on the Add an Alias option.

Step 5) After that, another prompt will pop up, here you will be creating your Alias. Under the Alias section, type the Alias you want for your email address. Then type your Full Name, in the label section just type Random or anything else related to your Alias.

If you wish you can also set the label color under the Label Colour section, pick one of the colors from there. Lastly, to confirm it and to create your Alias, just click on the OK button below; you alias has been created.

Step 6) Click on the Done button to close the prompt if you wish to disable the Alias just select the Disable alias box option and click on Done. To delete the alias, click on the Delete option, and confirm the delete.
Conclusion
If you wish to set up your newly created Alias on your iOS device, go to the iCloud option in the settings app. Then scroll down and open up the mail option. Under the Allow Sending from the label, you will see the aliases, toggle on the alias that you want to use.
To create an iCloud Alias, head over to the cloud website, go to settings>Preference>Account tab. Click on the Add an alias option and fill up all the necessary sections. Then click on the ok button, and you are good to go.