How to Type Special Symbols and Characters in macOS (English subtitles)

Shortcut to Character viewer: ⌃+⌘+⎵ (Ctrl+Cmd+Space)

I needed some special symbols to transcribe the words using Slavic phonetic script for my Polish course.
So here is the brief introduction to how to access all the layers of symbols on your keyboard and how to use the Character viewer on Mac computers.

It will work for other sets of symbols as well:
Unicode, IPA transcription, accents or diacritical marks, mathematical symbols, smileys and others.

Keep in mind that the font you're using has to support the symbols you type.
Microsoft Word on my Mac switches to the font that is supporting the symbol I type automatically but it depends on the program you use.