Learn Basic Coding

http://www.w3schools.com/

If you are new in Programming then the above site can be very helpful to you ...Learn Basic Programming Coding containing HTML, CSS, Java, VBscrpit, PHP etc. from the above mentioned site.

Check where is the error code in website

http://www.dmwvalidator.com/

http://jigsaw.w3.org/

http://validator.w3.org/

For Programmers, These sites can be much more useful to know their error in coding .......