subfolder not found

Hello. I do subdirectories
controller / Admin / Admin.php - CI did not see. He writes 404
models / Admin / model_admin.php - And I do not see it.
LAMP server

I suggest you follow capitalization very closely because it matters in CI 3.0. Class files must be capitalized.

Hey, don't work without a PHP debugger. Several free IDEs have this features built in. Two are NetBeans and CodeLobster. Without a debugger, it's like you're driving with a blindfold on -- you are going to crash!