One of the easiest way for me is this:
In the top right, click on the magnifying glass to do a search. Type "character" and press enter. It will open up the Keyboard section of the System Preferences. Make sure the box next to "Show keyboard and emoji viewers in the menu bar" is checked. You can close the System Preferences window.
Now notice on the top right again, left of the time, you should have a US Flag icon. Click on that and choose Show Emoji & Symbols. This will open up the Character View window. Here, you can choose all kind of special characters.