Definitely you should start with the latest version of Angular i.e. 6. About free resources you check this Angular tutorial video which teaches basic of Angular in 1 hour.
It covers like 16 chapters as listed below.
Chapter 1 :- Node and NPM
Chapter 2 :- Running first app & Angular CLI
Chapter 3 :- VS Code editor.
Chapter 4 :- TypeScript
Chapter 5 :- CLI project folder structure
Chapter 6 :- The config JSON files
Chapter 7 :- ng serve vs ng build
Chapter 8 :- Angular the binding framework
Chapter 9 :- Component and Modules
Chapter 10 :- Expression , Decorators and TemplateURL
Chapter 11 :- Declaration and BootStrap in Modules
Chapter 12 :- The main.ts file for module startup
Chapter 13 :- Index.html and the selector tag
Chapter 14 :- Polyfills
Chapter 15 :- Webpack :- Packaging and deploying
Chapter 16 :- Vendor.js and Runtime.js
solved Learn Angular 6 or Angular 5?