In MO2:
1. Click on the Wrench and Toolbar button on top of the mod tab.
2. Click "Install Mod"
3. Navigate to Downloads or wherever you downloaded the zip file to.
4. Double click the mod.
5. Tick the box on the left side of the mod title in MO2.
Manual:
1. Use a program like WinRAR to open the zip file.
2. If the folder is called "Data", just drop it in the main Fallout NV directory (where the FalloutNV. exe is located). The files contained within that folder will go straight to where they are supposed to be within the Data folder.
3. If the zip file contains folders called "Meshes", "Textures" and an esp or esm file, drag every folder and file into the Data folder.
4. If the zip file contains a folder named "Drag's NPC overhaul" or anything similar to that, open it. Go back to steps 2 or 3. Complete one of them, then skip to 5.
5. Go into your Mod Manager of choice and enable the esp or esm. If it is enabled it will have a tick next to it or a cross. You can also do this within the main FalloutNV launcher. Just open the New Vegas launcher (FalloutNVLauncher.exe) and go to "Data Files" and enable the esp or esm you got from Dragbody's zip file.