Free system disk space going out by itself

Hi forum! Thanks for your help!
I am having this free disk space problem that I'd like to understand. The message appeared quite some time ago. I had my thunderbird profile in the C disk, as well as some data. So, I moved it and deleted other stuff, and got myself bright beautiful blank space on the C, around 7gbs.-
Thing is it was a month ago or so, and now, the problem appears again. So, I am asking for a kind of solution, but in first place, I'd like to kwon what's going on.-
I have downloaded quite a few things, but they are in another partition. I always wipe off the temporal files, as well as internet temporary files. If I install programs, they are in another partitio too, but is not the case, for I have not installed almost anything(I know that even if we put the 'program' in a partition, some data goes in C nevertheless).-
I am aware of the existance of those progs that will show the ammount of data and its location and stuff. I have read mostly how to get rid of useless things, but I'd like to know what happens, and if I can prevent it from occuring.-
I have seen so far, with one of those that show the data, that the same archive can be located in both folders. That happened with the thunderbird profile files, which 1 gb would be 2 gb of disk allocation.-

Thanks again, and be well!

Hey!
Update:
I didn't do a thing, and I have now 3,5 GB of free space, out of nowhere. Any ideas?

Hey! Thanks for your answers.-
I am not interested in thunderbird, I just named it, my mistake. What I want to know is how windows manages the free space, and the reason for having lost about 7 gb of free space when I didn't do anything on it. I know how to erase things, and I have quite a few of those programs(thanks for suggesting one, I didn't know it). But I am not up to it.-
I mentioned thunderbird for it has quite large archives, and, I saw them duplicated. But the same happend with other files, I don't remember their names, they where .msi I guess(Install packages).-

So, I'll try to be specific:
1) How does windows manage free space?
2) What can I do to prevent it from using all the free space?
3) What happens when some free space comes back by itself?
As I said before, I had 3,5 GB(around 7 PM), and now(10 pm) I have 2,93 GB, and did not do anything, neither insalled a program, nor downloaded any file. I did not even entered web sites. I have been just listening to some music, and was no infront the computer.-
4) I am not willing to use the treesize kind of program in first place, for I am not trying to free space and get it lost again. Might I be a noob, apologies if that's the case, but I want the free space to stopo being consumed, not just erase things.-

Thanks!

Hi again, this thread shows quite my question:
Hard drive free space fluctuation...?
I'll consider downloading that tool the, thanks!
Remember I'd like to prevent the problem, i.e. free space going from 7 gb to 100 MB, back to 3,5 GB, again to 200 MB and so.-
And I'd like to add that the hybernation file is disabled, and the pagefile is in another partition.-