Save them in your Mods folder, that’s all there is to it.
Fancy having a go at changing some strings too? Perhaps you want to change the Mean trait to the Asshole trait, or rename WooHoo to Shag Like Bunnies or Tell A Joke About Dicks instead of Ducks. To do so, you’ll need to use S4PE to export the .stbl data from Strings_ENG_US.package (usually found in the C:Program Files (x86)Origin GamesThe Sims 4DataClient folder) and edit it with TS4 STBL Editor foundhere. Once edited, simply right-click the package, replace the .stbl data and save it as a new package in your Mods folder. I don’t recommend saving over the original, you never know when you might need it again.