I need an app that tells about file & folder sizes, like what is the biggest file and/or folder on my hard disk, sort this detail from biggest file and/or folder to the smallest & vice versa, also able to tell me about this detail based on the folder that I have chosen.
You could try Disk Inventory X.
Disk Inventory X is a disk usage utility for Mac OS X 10.3 (and later). It shows the sizes of files and folders in a special graphical way called "treemaps". If you've ever wondered where all your disk space has gone, Disk Inventory X will help you to answer this question.
I recommend DaisyDisk. Files and folders are visualized by a ring chart, makes it easy to identify which file/folder takes the most space in the hard disk.
The trial version has no limit on time, just a nagging screen when you launch the app.
You might be interested in GrandPerspective.
There are two GUI applications for Mac that help visually identify what's taking up disk space: Disk Inventory X and GrandPerspective. If you've ever used KDirStat or WinDirStat then you should be comfortable with it, but even if not it's fairly self-explanatory when you run it.
You can also search by file size in Finder.
My favorite is Space Radar (Electron-based, MIT license).