Hi, As Wahrheit says above, please refrain from posting twice in quick succession. You can find an "Edit" option near the bottom of your post, so you can simply modify your existing post if you'd like to add anything onto it. I've merged your two posts together, please keep this in mind for the future. Thanks, Sam.
Upon clicking the "Download" button, you will be presented with the option to download two files; you need to download them both. Head into SimCity 4 and create a new region; in this example, the region will be named "Eaton", then quit back to desktop. Copy and paste both of the downloaded images into Documents/SimCity 4/Regions/Eaton (replace Eaton with the name of the region you just created). Open up SimCity 4 again, and press Ctrl + Alt + Shift + R. This will make a new window appear. Within the new region, you need to navigate to your Documents/SimCity 4/Regions/Eaton folder, selecting the greyscale image from the download entitled "Eaton_Jhipolito.jpg", and then click OK. The game will then render the region.
If, for some reason, one of the above steps does not work, try using SC4Mapper to install your maps. Once installed, all you have to do is click "Create Region", select "Greyscale Image" format, and in the next window which opens, select the path to the downloaded "Eaton_Jhipolito.jpg" and also the downloaded "config.bmp" files.
Once you've subscribed to an item in the Steam workshop, you'll need to enable it in your game. To do this, click "Content Manager" on the ingame main menu, navigate to the "Mods" tab and then check the checkbox labelled "On/Off"