it sounds like yo have an SSD with a HDD. SSD are more expensive (so generally are smaller capacity), but are very fast. most people install their operating system (windows) on the SSD, aswell as software and maybe a game or something.
You should be storing everything else on your HDD. so move all your documents, music, videos, photos and downloads folder to your D drive.
(to do this, go to your C drive and click on it. then find the folder "Users", open that, then find the folder with your name or whatever name you used for your user and open that. then right-click each of those directories [download, documents, pictures, music, videos, and id probably do it with desktop too], go to properties, then go to location tab, and change the directory from C to D and click save. You can leave the path the same just change the letter from C to D and leave the rest. click the ok button. it will move the entire folder to your D drive and anytime you save files to that folder, it will automatically be on D drive)
*note* those are the only directories you can change using this method. if you want to change other system designated folders you will have to use different and likely more complex means. Any file not related to the operating system you can likely copy/paste to the D drive. (with installed software it should work, but some may not work and will need to be reinstalled to move to D drive)
that should free up a lot of space on your SSD (C drive).
Next you will want to clean up cache ands temp files and empty your recycle bin. You can do all this using CCleaner ( https://www.piriform.com/ccleaner/download ). its just 1 button to clean out all files you dont really need taking up space. (leave all settings for this software default. do NOT change anything unless you specifically know what you are doing). Id suggest running this software once every few weeks to prevent the ssd from being filled up with temp files.