If you need a desktop application that works offline, you must use an older version of the software. Microsoft Office 2016 (version 16.16.x) was the last major release to support OS X 10.11.6. Installer Links
: This older version also works but was retired in 2017 and may have more stability issues on El Capitan. Office 2008 for Mac : Still functional, but extremely outdated. Apple Support Community Free Options Microsoft Office For Mac Os X 10.11 6 Free Download
If you have an internet connection, you do not need to download anything. Microsoft’s web-based Office apps work perfectly in Safari on OS X 10.11.6. If you need a desktop application that works
Once the download is complete, follow these steps to install Microsoft Office: Office 2008 for Mac : Still functional, but
She wiped the screen and pressed the power button. The chime replied like an old friend. The login screen asked for a password she didn’t have, but a hint on a sticky note tucked into the keyboard — "June 2016" — nudged memory: the computer belonged to her college roommate, Aaron, who’d left it years ago when he moved overseas. She called him. He laughed, surprised and relieved, and told her to keep it. "It still has everything," he said. "Mostly essays, a terrible music folder, and Office for Mac."
Office 2016 is generally the most modern suite that runs smoothly on El Capitan. While Microsoft officially ended mainstream support for Office 2016, the software remains functional for basic tasks.