1) They will most likely come in .rar format. Download winrar, open up the mod rar.
2) Now open up your Fallout folder.
3) Drag all the files in that rar window (there might be a readme, but no harm comes from dragging that in) into your data folder. It will ask you if you want to replace, generally, just go ahead and do it.
You can then go under the Fallout Launcher, select Data Files and tick the little mod box.
Note: You'll most likely need to install the ArchiveInvalidationInvalidated (spelling?) mod, as well as the Fallout Script Extender. Most also recommend the FOMM (Fallout Mod Manager). Any advanced mods will need at least one of these, so just install them (pretty simple, all of them.)