How difficult is it to learn web programming ?

I have some programming experience due to my job but web programming fascinates me and I want to learn it for fun,how difficult is it and what are the programming languages or scripting languages I must learn to be a competent web programmer.

I have some idea of HTML and photoshop but all my previous web designing was done in WYSIWYG editors

Any suggestions ?

Thanks

i am curious how do error codes and error messages deal with html programming,did you even read my question ?