Conflict is what stands in the way of the protagonist's goal — the hurdles that must be overcome for them to get what they want. These obstacles can be a person, a situation, a personal struggle…anything that stops the protagonist from reaching their goal or doing what needs to be done.
There are two types of conflict: Internal and external. Internal conflict is the issue(s) your protagonist faces on an emotional or mental level. He loves the girl, but she's his best friend’s girlfriend. She has to have those new shoes, but can't afford them and stealing is dishonest. External conflicts are the physical things in the protagonist's way, things that involve action to avoid or escape. Confronting the best friend about his feelings for the girl, evading security to steal the shoes.
And you need both. Internal conflicts drive the character’s growth, external conflicts drive the plot. Attempting to plot using only internal conflicts will leave you discouraged, because there's nothing actionable thwarting your character from reaching the goal.
Too many times when I talk to authors about conflict they say, “But my characters are arguing. That’s conflict.” Not exactly. Sometimes fighting/arguing may be essential to deal with the conflict, but arguing with Joe isn't something that's standing in the way of reaching a goal. Your character might argue with Joe as a distraction to keep him from finding his girlfriend hiding in the closet, or to keep from being caught with the shoes stashed in her purse, but the actual fighting isn't the conflict.
As a beta reader and crit partner, I focus heavily on stakes (those of you who have had crits done by me can chime in here, heehee). Stakes are the motivating factor for your protagonist's goals, and why they have to overcome those conflicts RIGHT NOW. Yes, right now. Stakes are what happens if they don't succeed. Stakes are bad, and stakes are urgent. The higher the stakes, the more tension you build and the more gripping the plot. They are the "or else" in every risk.
There are two types of stakes: Personal and story. Personal stakes are what affect your character personally. They'll get kicked out of school, the antagonist will find and kill them, it goes against all they believe. Personal stakes are what really drives a story. They make the reader care about the outcome as much as the protagonist does. They keep the reader reading. They're also what's keeping your protagonist fighting when it gets tough.
Story stakes are what matters to the world as a whole, and many times, it's part of the story’s goal. If Clay doesn’t listen to all of the tapes, he’ll never know why Hannah committed suicide and why he was a part of it (yeah, I love 13RW). If Charlotte fights against her destiny as a Forgotten, others will die because of her (Suzanne Young does an amazing job of balancing both personal and story stakes in A Need So Beautiful).
One common mistake I see in the stories I beta read is that the character must decide between two things where the answer is obvious. Do something and the world is saved, don’t do it and everyone dies. That’s a no-brainer; of course he’s going to do it. Well thought-out stakes force the protagonist to choose between two things where both have a bad consequence. Another mistake I see is a character deciding between two things where either choice will give them the same result (the protagonist must decide between two really great guys). Or even a reward. Stakes should never have a reward. They should be difficult. And heart-wrenching.
Hope this helps! Happy writing!