Hello Landguy28,
It sounds like you are trying to free up storage on your Mac but because you are running OS X El Capitan, you don't see the Manage button when checking your storage.
To manage storage this way, you will need macOS Sierra or later as referenced in the Free up storage space on your Mac article you were viewing.
You can try to manually locate what folders are taking up the most storage by selecting Go > Home in the Finder menu and getting summery info, Get file, folder, and disk information on Mac for each folder. In Get Info, you will see the file size on the top right. In some cases it may take some time to calculate. Once you locate a particular folder that is using a high amount of storage, you can then open that folder and repeat the same steps to help isolate where this is located.
If you have a compatible Mac and want to upgrade check out How to get old versions of macOS.
Hope this helps,
Have a good day.