Opening an empty fiddle will give you the option to start fresh or create a fiddle from our boilerplates:
JSFiddle has the notion of panels (or tabs if you switch into the tabbed layout), there are 4 panels, 3 where you can enter code, and 1 to see the result.
HTML - structure code, no need to add
head, that's added automatically
CSS - styles. You can switch pre-pocessor to SCSS
Once you enter code, just hit Run in the top actions bar, and the fourth panel with results will appear.
Save / Update will do what you think, it'll save a new fiddle or update an existing one (and add a version number to it)
Fork will split out an existing fiddle into a new one, starting with version 0
If you're working a fiddle and updating it, the version number will increase, sometimes if you're satisfied with the code you have it's good to save it so that the version numbers are hidden, and the version you've set as base is the default one.
For example if you have a fiddle
jsfiddle.net/oskar/aba321/23 setting as base will make the 23 version accessible at