All the info Ты need on creating custom content, including a lot of tutorials, can be found at Mod The Sims (
link). However, Ты need to be really good at 3D modelling and have the right programs for it if Ты want to create stuff from scratch или modify the shape of existing objects. If Ты just want to do recolors, then Ты need a good graphics editor like Photoshop. Ты also need a program called SimPE to Редактировать the package files. If Ты go over to Mod The Sims and have a look there, it tells Ты all Ты need to know. But it's not easy - I had a go at just modifying the size of some hoop earrings to make them bigger, and it took days to get them working right!!