I have some executable files in OS X which I want to access from terminal from any area. For example in Linux, we can copy executables or binaries to /usr/local/bin or /usr/bin. So similar to that where can I copy executables in OS X? I have downloaded Firefox and copied it to /Applications. Now I want to execute Firefox from any area without going in to the /Applications.
/Applications is the central repository for installed Applications on OS X, you can put any executable anywhere and launch them from anywhere within terminal so long as its directory is in your path.
The question is, why exactly do you want to launch things like a browser, which is graphical in nature from the command line?
If you just want to type the name of the application, simply invoke Spotlight by pressing Command+Spacebar and start typing. It's how I normally launch apps that I don't have in my dock.