Welcome to the next guide! Have you named your character yet? You should've also made their description beforehand (hint, hint). Once you get those two done, guess what? It is time to develop your character, possibly the hardest part of writing one.
Personality // Explanation
So every character has a unique personality. You need to start out by planning your main character, and then all the other characters excluding minor ones that appear like one time (unless you have a secret plan for them >:)) But don't freak out! Good stories take a lot of planning. So decide what personality type and character traits/qualities your main character has.
There! You can just make them grumpy, angsty, and self-hating. But why? Why are they like that? What made them become this way? For extra effect, what if they weren't always this way? (Yes, some of you know I'm talking about a certain someone shh) The point is, give them a valid reason to be this way. Don't use cliché backstories or what everyone uses for this type of character. Make up something different. Something that would make YOU change that way.
Now if you're banging your head against your desk at this point, I get you. All you ever wanted was to create an awesome story for readers to love so much like you love a certain series so much. But a backstory is mandatory for every character (again, excluding minor characters you don't have any plan for.
Have you chosen your personality? Good! Time for the backstory. Now, if you're starting your character off as a kit, don't be panicked! You can use this as an opportunity for the beginning of your main character's story. But even if you aren't starting off from when your character's a kit, you still need to show the backstory in the plot - whether flashbacks, brief mentions, and so on.
So suppose your character has a loathing for...um...dogs? And they're scared of tree-climbing? Why not connect these two? Maybe as a kit, they were a rogue and a dog attacked their family so it's parents put it up on a tree to save it's life and they were killed instead. See how that makes sense? I would assume this character's personality is "they're kind of a coward, scared of things that lead back to that one incident, they also want to protect their mate and kits (their new family) from dangers like that ever again" That would be the usual. Try adding more traits that fit in well with this assumption as a character outline.
So how does your character interact with others? Are they hostile?