How can you make your own custom objects for The Sims 2?

Photoshop

Creating your own Custom Content for The Sims 2 requires the use of third party software, such as 3D Studio Max, Photoshop, and/or others.

Creating objects are extremely difficult and really not feasible as there would ultimately be no animations for the Sims to "use" the object in the game.

Recoloring other objects, or improving on existing objects, are somewhat more likely because the animations are already there and associated with that particular object.

Creating new hairstyles, makeup, skins, eye colors, clothing, shoes, accessories, and other parts of your Sim that can be "worn" isn't as difficult, but it does require lots of time and skill on part of the creator. You can also recolor existing clothing, hair, and etc to create "new" ones to add to the game as Custom Content.

There are few tutorials on how to create Custom Content because it is such a difficult process for those who do not have that skill and/or ability already. Try searching for your particular tutorial on google.