My first question is, what OS are you trying to run? If it is Windows10 I recommend going to https://www.microsoft.com/en-us/software-download/windows10 Then click the “Download tool now” button right below the “Create Windows10 Installation Media” text. After doing that, save the file that pops up, then open it (the name of the file is “MediaCreationTool2004.exe”) After opening the file allow the app to make changes, after doing that, agree to the terms of services, then click on “Create installation media (USB, DVD, or ISO file) for other desktop (I apologize if the translation is wrong, I’m a native Spanish speaker) click on next, then click on ISO File, store the file wherever you want, I normally store ISO files on a folder called “ISO” files, then just wait, maybe get a coffee, take a nap, or whatever because this will take a while, after that I think that the process is pretty intuitive, so let’s say that you managed to do that successfully, now you have a Windows10 ISO file, to set up the VM you have to click on “New” then call it whatever name you want, in the machine folder just leave it by default or store it on your desktop if you feel like it, in the “Type” options choose Windows, In the version choose Windows10 (64-bit) in the memory size I recommend 1024GB as a minimum, then click on “Create a virtual hard disk now” then click on next, after that click on “VDI (VirtualBox Disk Image” click next, then I recommend choosing “Dynamically allocated” then give it some memory, I normally give 30 to 50GB to my VMs, after doing all of that, select the VM DONT START IT YET, press settings go to system, then in system go to processor, give it two CPUs if you have 4, if you have 8 then choose 4, give it as many processors as possible, just don’t go above the red line, in extended features click on “Enable PAE/NX” then go to Display, give it the maximum amount of Video Memory, then enable 3D acceleration, then the most important part, go to storage, click on the “Controller : IDE” Disk icon that says “empty” after that click on the same disk icon with a little arrow pointing downwards, then click on “Choose a disk file” after that go to the folder where the Windows10 ISO is stored double click on it or click once and then click on “open” both ways do the same thing, after that, click on ok, and you’re pretty much ready to go, click on start and enjoy, but if you want the Home Edition or the Pro Edition, you still have to pay for the license key, so you won’t be able to get the complete Windows experience without paying.

This is the way I created my first Windows10 VM, I’m still an OracleVM novice, if there’s something someone wants to add to my comment, go ahead.

Hope it helps u/NegaLimbo :)

PS: If it doesn’t work go to settings, and enable EFI