Ok im not gona go very far into this cuz i gota go cut the grass (if you know what i mean 😉 ) neway. Html is supposed to be coded semantically so like use the elements for what they were intended for. like you want a paragraph of text use the <p> element. you want a list of infomation use either the <ol> or the <ul> element,
you want a table of infomation? use a <table> element.
You get what im saying here? if not google "html semantics tutorial", infact do it anyway.
Ok now CSS stands for Cascading Style Sheet's.
think of it like this. Html is for defining the documents structure. whereas CSS is for stylizeing the Html (creating a visual aspect...)
ok now this is a good site HtmlDog.com
use it for a reference of HTML and CSS as it has list of html elements and examples of their use and it also has an entire property's reference for CSS 😃
hope this helps.