What do I need to learn to do this (web)

I'm wanting to be able to create a website that can do this:

Take information from input types (drop down lists, check boxes etc). Pass that information back to my server. Compute information on it, based on information chosen in the input forms and also based on information in a database (that I'll need to create and will need help there). Pass the resulting data back to the site and update it (with text initially, nothing fancy). I already know html and css well enough to create the visual content of the site (infact it's already done). I'm fairly competent with javascript, so can do all the compute easily myself. Also fairly competent with SQL. What I'm unsure about are the technologies I'll need to learn to do everything else.