I bought the car from someone I know. He took great care of this car, it was 'his baby', but now it's mine

I was not a fan of the decals, must admit, but that changed after an 8 year old boy that the car was 'cool'.
I love learning all of the new features of the vibe, so excited to join this forum!
Silly question, but since I don't have an over drive button in my car, does this means the car gets into overdrive automatically, depending on the gear I'm in?..
After speaking with a friend yesterday, I learned that staying between 2/3 RPMs helps the car do less work, smoother ride and helps save gas. Is this true?
So I have been driving it in 4th gear, and 5th if its over 60
Looking forward to hearing from you!
-Velarey