The games in the series generally lack defined goals, unlike most other video games. The focus of the games is on the simulated lives of virtual people called "Sims". The player is responsible for directing their actions, attending to their needs, and helping them attain their desires. Players can play with pre-existing Sims and families, or create their own. They can place their Sims in pre-constructed homes or build their houses using the in-game building tools, then furnish the homes with objects from an in-game catalog. Numerous add-ons and expansion packs greatly expand the number of features, tools, and objects available to play with.