Can anyone point me to a good tutorial pointing to how to get unique spritesheets to work

[Duckfromportal]

Hi everyone, I am working on a mod to add a daughter to Willy and have hit a snag, I don't actually know how to get my sprite to show up, I used Willy's and Abigail's Sprite sheets as a reference and made the character Sprite sheets for both winter and for normal time, but I can't seem to figure out how it works for putting it in the game, are there any current tutorials for