Typically in Unity 3D, you would create explosions through a combination of different assets being attached to a Game Object. It can be a time consuming process with lots of trial and error involved. I found out recently that Unity offers a package that can be imported into your project called Detonator, which can be downloaded here. The package comes with documentation about the Detonator framework including some of the commonly used functions that can be utilized to script the explosions in a way you want.
The detonator package is pretty expansive. It comes with sound effects, particle effects, scripts, and Game Objects that come with a plethora of variables that can be tweaked and modified to get exactly the kind of explosion you want. The basic workflow is that you would attach a detonator asset to just about any game object that you want to have an explosion on. You can use detonator functions in your scripts to tell the explosion when to detonate depending on factors such as collision or health, physics, etc. The most common function you will use is the Explode() function, which is talked about more thoroughly in the documentation that comes with the detonator package.
In order to bring Detonator into your Unity project, you will first need to download it and save it to a location on your hard drive. Once it’s saved, open up your Unity project and go up to “assets” → “Import Package” → “Import Custom Package…” → Browse to the place you saved the package to and double-click the Detonator.unityPackage file. This will bring it into your project for you to use. You should see it listed in your project view.

Check out this basic demo of what detonator can do:

Learn more and watch some basic Unity video tutorials. If you are looking to really learn industry-standard tools like Unity, Autodesk and Adobe software design3’s video tutorials can help you master game development and 3D animation