Can someone kindly give a short explanation of how SharePoint column validation works. As I tried to validate one column I didn't know if its working or not coz I wasn't getting any error message or anything, the forms was just not submitting at all
Here is a link to all of the information you will need for creating validation on columns. This link goes directly to Microsoft's site where it explains how to format your validation statements for whatever it is you are trying to do. It also explains what they do and how they work.
If you have column validaiton on, like the Title field is required by the checkbox, it will run those first, then it will run your validations you make in the validation settings for your columns. Fill in all required fields by checkbox first, then see if your validations run.