I have an Asus s200e laptop running Windows 10, and it has a C and D drive. The D drive is never in use by Windows, so I want to put Linux on it, how do I do so without deleting anything? What should I make sure to do? I am fairly familiar to Linux, just not so much partitions. Thanks!
I would suggest that you shrink the D drive and free up the space in which you want to install ubuntu, go into device manager - disk management and shrink the D drive, then unallocate the space where you want to install ubuntu & you can safely install linux. This way you will also have some part of D drive to store data and some part which will be utilized by linux. But make sure that you leave sufficient space for ubuntu installation.
Good luck Dual booting.