Unicode Consortium, a non-profit organization maintains technical specification for all emoji symbols. Fundamentally, you can type all emoji symbols similar to text characters. However, default keyboard does not have keys to support thousands of emoji and other symbols. Therefore, you need to use alt code shortcuts for inserting symbols or use other tools like Character Viewer in Mac and Character Map in Windows 10.
Alt key is one of the modifier keys available on both Windows and Mac keyboard layouts. You can use alt key along with decimal and hexadecimal codes to type symbols and special characters. This website offers thousands for alt code keyboard shortcuts for Windows and Mac along with HTML escape entities.