Instructions
Go to a "Sims 2" mod repository.
Click "Download," "The Sims 2" to go to the sites' specific "Sims 2" custom content pages.
Browse the options until you find content you like. Alternatively, if you already know the name of the file you're looking for, type its name into the search bar.
Click the download button. On Mod the Sims, the button says "Download." On The Sims Resource, it's an arrow icon pointing down. The Sims Resource also requires you to be logged in. Register for an account by clicking on "Register for Free."
Unzip the mod. If it ends with the extension ".package," drag and drop it into the "Sims 2" custom content directory, "\My Documents\EA Games\The Sims 2\Downloads." If it ends with ".Sims2Pack," double-click on it and then click "Install."