This excellent question has two answers...
1) You should take this beginner guitar lesson online because you're now going to learn for free what a teacher would charge his normal hourly rate to tell you.
And even if he did have the patience to clearly explain all this for his ninth time today, he'd probably tell you in such a rush (so that he could get to the "real" instruction) that this critical beginner guitar lesson would go past you in a blur. When you got home, you'd wonder just exactly what it was he had said.
So right off the bat you've saved at least a one-hour session with your teacher (probably a minimum of $20, depending on where you live) to get these foundational guitar tips here instead of in his studio.
2) Another great benefit of taking this free guitar lesson online is that you can come back to these guitar tips again and again, at your convenience, to review and solidify what you've learned.
After all...Repetitio est mater memoriae
(Latin - "Repetition is the mother of memory")
And now let's take a beginner guitar lesson online...
In my teaching experience the first questions beginners (or their parents, if they're younger students) ask over the phone and in the first lesson fall into these catagories:
"With what kind of guitar should I (or my son or daughter) start lessons?"
Compare Acoustic and Electric Guitars
"I've decided what type of guitar I want. Now what do I need to know before I go into a music store to actually buy one?"
Purchasing Your First Guitar
"My new guitar sounded great in the store but now it sounds awful. Should I return it?"
How to Tune a Guitar
"It feels awkward when I hold my guitar, my fingers hurt when I practice, and sometimes I get a pain in my wrist after I play for a while. Am I doing something wrong?"
How to Hold Your Guitar, Why You Should Hold It That Way, What to Do About Your Hurting Fingers, and Exercises to Protect your Hands and Wrists
"My favorite guitarist is (fill in the blank). How long before I can play better than he or she can?"
Reaching Your Guitar-Playing Goals
"What are the names of all the notes I can play on my guitar?"
Guitar Fingerboard Charts
"What are chords, and how do I play them on the guitar?"
The 13 Most Useful Guitar Chords for the Beginner
"I've heard a lot about something called 'guitar tab'. What's guitar tab, and what do I do with it?"
"What's Standard Notation, and why is it important for guitarists to learn how to use it?"
"Time Signatures are easy, right? The top number always tells us the beats per measure and the bottom number always tells what kind of note gets the beat. That's how it works, right?" Wrong. If this is how you learned time signatures, you definitely need to take this lesson...