A barrier block is one of the coolest blocks available to use in Minecraft, however, it can't be accessed via the inventory tool kit. A barrier is an invisible block that that players can not go through.
To give yourself a barrier block, you must use a command to place it into your inventory bar. Depending on the device you have, there are various ways of accessing the chat/command bar. Essentially, it looks like this:
In this chat/command bar, enter /give @s barrier (including the forward slash). Then hit the arrow. This will give you a barrier block (pictured below). If you are in Creative mode, this command will give you an infinite number of barrier blocks.
