First, some background information.
In Windows, C:\ is your primary drive, where your operating system (Windows) resides. By "drive", I'm referring to either a Solid State Drive (SSD) or Hard Disk Drive (HDD).
By default, C:\ is also where your user profile(s) reside, where your applications are installed, and so on.
If you have additional drives, they'll be labeled D:\ E:\ F:\, and so on. If you have an internal optical drive (CD/DVD/Blu-Ray), traditionally it would get labeled as D:\ but not all computers come with one of these anymore so your system may be different.
A lot of gaming computers will come with 2 drives. The primary drive is a SSD, for the operating system and applications. The secondary drive is a traditional HDD, mainly for user data - your documents, videos, photos, etc. The reason for this is that SSD is a lot faster than a HDD. However the downside is, SSD is a lot more expensive compared to HDD.
Looking at the first image you posted, your system seems to be using this configuration of a SSD for its primary drive and a HDD for its secondary drive.
Now then, on to your issue, which is really "I'm running out space on my C:\ drive"
First of all, do NOT simply copy or move applications by yourself. That simply will not work. Installing an application on Windows puts some files into different system directories, as well as a bunch of settings into a special system file called the Registry. While it IS possible to move an application from one drive to another, it requires a special program to do this, and isn't always successful.
In most cases it makes more sense to leave your applications on your SSD - they will load faster. That goes for games as well. So you should just leave them alone on the C:\ drive.
For things like downloads, you can (and should) change where files are downloaded by your browser(s). This is in the settings. For instance, you can make a directory on D:\ called Downloads, and tell your browser(s) to use D:\Downloads for downloads.
For simple files - downloads, photos, documents, etc. - you can simply drag & drop to move them from one drive/folder to another. That should free up some space on your C:\ directory.
Other tricks to clear up space include:
* Right click on your trash can, click on Properties, and set the trashcan space to something small, like 100MB instead of 10% of your drive.
* Regularly delete temporary files. Do this under the settings menu of your web browser(s).
If you are still worried about the amount of free space on C:\ see if there are applications you do not use and uninstall them. Good candidates include any demo or trial versions of software that so many computers come with pre-installed. If you have other applications you need but don't use very often, consider putting them on the D:\ drive. To do this, uninstall the application, and then reinstall it. During installation you will be asked where to put the application. Instead of the default, put it on the D:\ drive somewhere. (e.g. D:\Program Files\)
If you are using Steam, it is possible to use the Steam client to move your Steam directory to a different drive. This way you won't need to redownload your games. Just be aware that you may notice longer load times since a HDD is slower than a SSD. I'm not sure what the procedure is for other services such as Origin, check their documentation.
Finally, if you have purchased a game through Steam or some other online service, you can delete a game and re-download it at a later time without having to buy it again. After all, purchased games are part of your account. So don't worry about deleting games if you need space.