How Do these people create Custom hair and Etc?

I saw these people creating custom hair clothes and makeup but how do you create it?a href="http://thesims2.ea.com/exchange/sim_detail.php?et_id=1397162&searchPage=exch&search=1&et_type=sim&key=clothes&order=CREATION_DATE+desc&nrows=8&game_version=&age=&gender=&custom=&locality=&country=&view=new&hideFramework=&languageCode=" rel="nofollow"http://thesims2.ea.com/exchange/sim_deta…/a