If you're using your mobile phone as a Wi-Fi hotspot for your Windows PC, or just trying to stay within a data cap from an internet service provider, you'll want more control over what things get downloaded and when.
First of all, you can easily see in Windows how much data you've used. In Control Panel --> Network and Internet, there's a data usage tab. This will show you how much data has been used and which apps have been using data.
You can also set a limit to how much data will get used by Windows. Open the Start menu and choose Settings. Then click Network & Internet --> Wi-Fi --> Advanced Options. In here, you'll see an option for setting a "Metered Connection." When you turn that on, it will disable Windows updates from automatically downloading, app updates, and Live Tiles won't update.
This will ensure that Windows won't use data unless you initiate it. Watch Leo's explanation of limiting data use in Windows here.