If a person or a designer wants to export a font file from Adobe Illustrator, how can he or she so do to make it a TTF or OTF file?
As alredy commented, a piece of font editing software inputs your Ai file (or clipboard) and places it as a glyph into a font. There are Fontographer, Type Tool etc... as examples of commercial products. Free font editing software is also available.
Font editing software is complex and often it's well underestimated, how much effort it takes to create a proper complete font. If you're fast and accurate in Ai, that surely speeds the font creation process. Vector drawing and editing tools in font editors are rudimentary when compared to Ai.
Your question can have also another answer. You may want to copy a complete font that is available in Ai, but cannot be found in the Fonts folder of your system. This is because commercial font suppliers, for example Adobe put a substantial amount of effort to prevent users to distribute their fonts or to use them without paying the wanted price.
In that case you should buy or hire the font for use in the system to where you originally wanted to copy the font.
Note: Adobe CC stuff should be available for you in two of your computers, but not simultaneously, if you pay only for one license. You can install the CC stuff for ex. into your desktop workststion and into your laptop or tablet.