I'm trying to get elementaryOS working on Virtualbox to test it out, so i took it from the OSArchive website, but now i'm confused because i get the "iso" on winrar, but there is no iso file! And there's also all these files and documents, so can someone tell me, what or where is the iso file? (Note: I tried to put in the efi.img file with floppy controller but it didn't work so i'm even more confused...)
The iso file you downloaded is NOT supposed to be opened with WinRar. To achieve what you want, you have to open VirtualBox, create a new Linux machine and, at the first startup, point it towards the iso file you downloaded. Take a look at the gif below for a quick tutorial (better quality here). When creating the virtual machine, I suggest allocating at least 2GB of RAM if possible.
After installing elementary OS inside your new virtual machine, you should also install VirtualBox guest additions (better mouse integration, improved video support...) This tutorial is for Ubuntu, but it will work just the same for any Debian based Linux distribution.
Here you can find a detailed step-by-step tutorial on setting-up a new Linux machine.
As a side note, elementary OS performs a bit unsatisfactory in VirtualBox, so the experience is not really as good as running it on real hardware.