Difference between read & execute, file permission

Folder Permissions:

• Execute -> Actually enter that folder but not be able to read it's contents, see what files are located there.
• Read -> Be Able To Read Folder Contents
• Write -> Edit folders data. delete or create new files/folders inside it and etc

File Permissions:

• Execute -> if it's script like index.php run it to get data from it
• Read -> if it's text file like index.html or index.php be able to read it
• Write -> ability to change its data

As for security, this permissions are only an issue when your server is accessible by other (not from your team) users and this was mainly happening when people where using hosting services where they were not getting dedicated operating system but there was one operating system and all the users where uploading their data there. So if not correctly secured, they could view and edit each others source codes.

Today as usual you get dedicated server, with more security tools and operating system which is accessible only by you and no one else (virtualization).

So you don't need to worry that someone will view or change your data as you are the only one who has access to that server.