-Place the main folder "RTH" in Steam\steamapps\common\Rome Total War Gold folder
-Go onto steam and where your RTW game is right click-proporties / then click on set launch option / then paste in everything that is red / -mod:RTH -show_err / The "-mod:RTH" is looking for a folder called "RTH" from which to load from, the "-show_err" will display a message detailing an error that you've encountered.
If you are not fussed about the error message you can just paste / -mod:RTH /
Make sure that there is no space before the command.