How to install Internet Explorer on Mac OS X 10.11.6 ( EL Captain OS ) ?
IE hasnt' been available for Mac since version 5.x. Your best depends on your needs: cheap PC, Virtual PC, Parallels, different browser on Mac.
What are you trying to accomplish - what need do you have for IE on Mac?
The last native version of Internet Explorer for Mac was IE5, in about 2003.
There are two ways to run a more current version
using a VM running Windows, or
this intriguing way to run it using MS Remote Desktop Connection & the Azure RemoteApp - admirably explained by OSXDaily - too much for me to précis here & not something I can test, as the current RDC beta no longer has the Azure tab.