The usage of symbols and special characters on Excel is about its purpose. These symbols, and special characters are extremely useful for different things. I will show you where you can get the symbols, and special characters that you can use.

Click on Insert tab.

ribbon insert

Click on Symbol.

ribbon symbol


Note: If the symbol is showing in grey, just click on the cell you want to insert symbol or special character in, and it would stop showing grey.

Choose Symbols or Special Characters (1), and then click on desired symbol or special characters (2), and then click Insert.


Further reading: 
How to deal with special characters in formula?
Sorting a list of words by character count