Reason and Persuasion
Thinking Through Three Dialogues By Plato

High school philosopher resource: here (also linked by u/robeschi)

Sample Syllabus: here

A concern with some of the above course outlines/readings would be that... well they're pretty ambitious, especially for someone with no familiarity with the material.

You might start with any one of the recommended anthologies and an introductory philosophy MOOC, to get a feel for what interests you and what your options are. See here & here for intro MOOCs.

The 2nd MOOC above, 'Reason and Persuasion', has a beautiful, fun, easy book available for free here. The book contains new translations of three dialogues written by Plato. These translations are very colloquial. And it fits the style--they're dialogues after all. The translation and the book as a whole have gotten good reviews. There is simply no way you're not going to leave important people/ideas out, so taking a deeper dive into Plato, the father of western philosophy, might be right for you.

Excellent recommendations from u/onedayfourhours, I am going into some of these, but I will give you my plan, as a beginner, what I have set for myself. I wanted to set this as series of courses, asa I think it will be interesting to have a predefined path someone was thinking about, and some of these is giving additional resources within each lesson, possibility to discuss what you have been listening to, etc.

Intro to Philosophy MIT's 18-lecture course, it starts very interesting and is improving from there.

Critical reasoning for beginners - YouTube University of Oxford's 6-part course on Critical Reasoning.

A Romp Through Ethics for Complete Beginners - YouTube Same university

Philosophical Problems - Free Course by La Trobe University on iTunes U - Introduction as well, but covering different philosophical topics then MIT's one.

I will then follow with a course on Plato. So far, I have read few of his dialogues, but will return to them and go in more structured fashion:

Ancient Philosophy: Plato & His Predecessors | Coursera

Reason and Persuasion: Thinking Through Three Dialogues By Plato | Coursera

These should finish my "semester 1", I already have further plans, with courses to cover Roman philosophy (Seneca, Cicero) and continue with some medieval and Christian thinkers, going on further until 20th Century and existentialism.