Creating validation for user input via visual basic code?

Hi,

I have 5 fields on my form which I need to validate on lost focus and save button. These fields must be mandatory. Searching through google I have find useful tutorial

http://www.codeproject.com/Articles/13922/Validate-user-input-in-Windows-Forms

but I don't want to install some "Validator.dll" in order to achieve this, I want to have code on lost focus event and save button. How can I do this for 5 fields?

Any help is appreciated and many thanks in advance!
Adi