Character and plot development are totally entwined. Each is wrapped around the other, like the double-helix DNA of the story. Each is each is dependent upon the other, but at the same time, is made possible by the other.
When you begin your story you have:
- A character who has some growing to do, and
- then, a situation in which your character finds himself.
Sorting out that situation will both require, and facilitate, the character's growth.
As each event of the plot happens, the character will grow a little to be able to cope with that event, and so the plot development leads to character development.
But equally, as the character grows in strength (whether that's literal strength, or emotional strength), he will push the plot forward by overcoming obstacles and being proactive towards seeking his goal. This leads to the rising action of the story. Tasks your protagonist would never be able for at the beginning, they are able to tackle as the story develops.
So process of the progression of both character and plot is truly entwined.
It's actually very elegant and beautiful.
I suggest you read some good novels with a view to analysing how their authors skilfully meld these two aspects, each contributing to the other. And look at your own stories too, to see how this process is happening.
You can do it the other way around too, which can help with the writing process. If you're stuck in your story, ask yourself if what's needed next is some character development, or some plot development. Whichever one of these it is, it will cause the other to happen too.