Processing is the thinking that the computer does - the calculations, comparisons, and decisions. People also process data. What you see and hear and touch and feel is input. Then you connect this new input with what you already know, look for how it all fits together, and come up with a reaction, your output. "That stove is hot. I'll move my hand now!"
The kind of "thinking" that computers do is very different from what people do.
Machines have to think the hard way. They do one thing at a time, one step at a time. Complex procedures must be broken down into VERY simple steps. Then these steps can be repeated hundreds or thousands or millions of times. All possible choices can be tried and a list kept of what worked and what didn't.
People, on the other hand, are better at recognizing patterns than they are at single facts and step-by-step procedures. For example, faces are very complex structures. But you can identify hundreds and even thousands of different faces with just a glance.
A human can easily tell one face from another, even when the faces belong to strangers. You don't recognize Mom's face because you remember that Mom's nose is 4 cm long, 2.5 cm wide, and has a freckle on the left side! You recognize the whole pattern of Mom's face. There are probably a lot of folks with noses the size and shape of Mom's. But no one has her whole face.
But a computer must have a lot of specific facts about a face to recognize it. Teaching computers to pick Mom's face out of a crowd is one of the hardest things scientists have tried to do yet with computers. But babies do it naturally!
So computers can't think in the same way that people do. But what they do, they do excellently well and very, very fast.