so I want to learn Filemaker pro and don't need the latest since I'm not that sophisticated.
sophistication doesn't matter. FileMaker 15 is not terribly more sophisticated than filemaker 10 was. The fundamentals are essentially the same.
But what IS important, is that in no way shape or form, is filemaker 10 supposed to be compatible with El Capitan.
The support period for v10 is long since passed:
So you should be updating just for the sake of using software that was designed to work with a current OS.
I don't know how to get around your error, sorry.
I got a disk a used computer. Mac OS X Snow Leopard apple Internal Use Software. It has a copy of Filemaker Pro 10 Advanced. I am helping a friend catalog her dad's artwork, so I want to learn Filemaker pro and don't need the latest since I'm not that sophisticated.
I copied the folder into my Applications but when I tried to open and intall it, I got this message:
FileMaker Pro 10 Advanced can't be opened because it is from an unidentified developer.
Your security preferences allow installation of only apps from the Mac App Store and identified developers.
“FileMaker Pro 10 Advanced” is on the disk image “fmpa_10.0.3.303.dmg”. Safari.app downloaded this disk image on July 15, 2009.
I went into my security settings and clicked open anyway, but I get the same message. I am runnin OS X El Capitan Version 10.11.4. Any advice?
In addition to everything Mike suggested (which is all true), I'd also remind you that FileMaker Pro 10 uses the old .fp7 file format and if you did do some work for a friend, that file would need to be converted to the .fmp12 file format. While that shouldn't be a problem, it is some unnecessary overhead you don't need to do if using the latest version.
As for the error you are seeing, what happens if you right click / command click on the FileMaker Pro 10 application itself and choose OPEN from there? This sometimes allow you to get past the security warnings you reported.
But as previously mentioned, FileMaker Pro 10 is old and is not certified to work with El Capitan so you'd be swimming without a lifeguard if you got it to eventually work. Unknown issues could occur which would be a shame if you put in any time on development.
There is always the 30-day trial of FileMaker Pro 15 if you want to get your feet wet.