I have been playing piano for a few months now, and I have come to a roadblock, in this one song I play CDEFG C on octave 4, while I do the same on octave 5. All of this is with one hand, I have been using my thumb for octave 4 and my small finger for octave 5. I find it pretty hard, I keep missing notes and having trouble adjusting my fingers to play these notes. Am I doing anything wrong, or is this just a thing I need to practice? Sorry if I am a bit unclear, I don’t know many piano terms as I have been teaching myself.
Since, with octaves, both notes are always the same distance apart, get a goood span, and don't change the shape of your hand. you only need to look at the top or bottom note, and the other will play the corresponding octave. I suggest watching the thumb.
Articulate from your wrist, and move your whole arm laterally at the right speed to arrive at the next notes, and instead of moving your fingers, move the whole hand up and down in a pecking motion. Slowly, and with lots of practice, it'll come. Although, as musicamante says, there are many other techniques that should be learned before that one.
That's just practice.
Depending on your hands, you may also try with thumb and ring finger.
But consider that if you've been learning piano for such a short time, there's a ton of other things to learn and practice before playing octaves.
I mean, it's not like it's forbidden, but it's almost like focusing on long jumping while still learning to walk.
It will require time and lots of more important milestones have to be reached before being able to do that, so don't get too mad about it, as you could even risk to injure yourself or learn with a bad technique that could become difficult to re-educate.