You take a look and are confronted by this shit:
"wtf this is like an accountancy PhD"
Sooo.. Do you need to learn all that by heart?
No. NO! Seriously, don't.
However, some of it can be useful to learn as needed.
Soon after you start playing you're going to run into a situation where you are wondering how fast a certain move is. For example... Well, fast moves beat slow moves, right? Because they hit earlier. If you start at the same time.
What's your fastest move? What's your fastest mid-hitting move? How fast is u/f+3, this spinning kick thing you like to use a lot? Those are useful things to know.
Frame data can be a tool to help you with this. Time in fighting games is measured in 'frames' and there are 60 frames in a second. So 'how fast' is that move you just did? Well, it can be expressed in a certain number of frames.
Start up frames are a measure of the time from the start of a move until it hits.
That jab there has 10 start up frames. It takes 10 frames for this jab to hit, so 10/60th of a second.
As a new player, all you should care about is that this is a more useful and precise way to talk about speed than nonspecific stuff like 'pretty fast i guess'.
"This move is 10 frames which means it is faster than some other move which is 15 frames. If you start both at the same time, the 10 frame one will connect first."
That is all. It's not too hard to understand, right? Time is best expressed in numbers, and frame data is those numbers for a fighting game.
Still, you don't need to learn frame data if you don't want to. You can figure out which moves are fast or slow by just playing, by trial and error. Or you can look at the actual numbers from time to time, as needed. Either way, you'll be okay.