Standard answer: imaging.
That can be done with the built in Windows Backup and Restore program or with third party programs such as Macrium and Acronis.
Most would tell you that Macrium and Acronis are more flexible and easier to understand. Macrium is probably the simplest to use.
There are tutorials on this site.
The free version of Macrium is all you would normally need.
Get it here: Macrium Reflect FREE Edition - Information and download
If your C drive has 50 GB occupied, the image file Macrium makes will be somewhere around 25 GB in size. You need to have some other partition on which to store that file---D, E, F, whatever. Preferably on another drive entirely, not just on another partition on the same drive. Most people use an external drive for that purpose.
In addition to C, you need to back up System Reserved, if you have such a partition.