Downloading server files

How do I make it so that whoever joins my server ONLY needs to download everything inside of: “/gamemodes/dew” file. (the gamemode is called dew)

Thanks in advance,

Use AddCSLuaFile() for any shared/client side files you want a person to download.
For other resources such as models/textures/sounds use resource.AddFile.

They need any client/shared files that your gamemode has.

How do I add the texture resource code?
Where do I put it?

In any server side file …

You can read all about it on the wiki.