I'm interested in learning the vulgar latin language is there any website that teaches it? Does the classical latin and vulgar latin have similar words or the words are completely spelled differently?

Hi all !
My question is how different are the classical version of the latin language and the medieval one ? I know that medieval latin varies from country to country so I will specify that I'm talking about medieval latin in England ( Britain ).
I'm asking becouse I'm currently studying the english medieaval latin and I have never studied classical latin before. I know that medieval latin was derived from vulgar latin but I don't know much about it else from it was spread to the foreign provinces by the soldiers. I don't know how related is it to the true latin. Therefore with the knowledge of medieval latin will I be able to understand the language of the late Roman republic and empire or not ?
I'm looking for both dictionary and grammar and further explanations would help.

Ok, so, if I want to learn Latin, where do I start?

I want to learn Latin in order to have the foundations to ease the learning of the romance languages. If I learn Latin though, I would obviously want to read some great works in Latin (or at least try, lol). So, is there a distinction? I ask because im under the impression that vulgar Latin is the root of the romance languages, but that it differs from written Latin. So...I want to learn Latin: Where do I start?