oracle vm virtualbox install guest additions ubuntu

I'm really new to doing anything with a computer other than browsing, so if you want any more system/log info I'll be happy to provide it but I would appreciate some instructions for finding it, if possible. If anyone can explain it to me like I'm a primary schooler, I'd be really grateful. I have seen lots of people ask the question but they've been installing on Linux or Ubuntu, or the information in the response is really technical. I tried to set up a shared folder but the VM informed me it wouldn't work because Guest Additions isn't installed (so there's my proof).

I followed the setup from a YouTube video, and they got a notification. However, when I open the VM and click 'Install Guest Additions CD Image' it does nothing. I have successfully installed all of the above files.

Browse to C:Program FilesOracleVirtualBox and double-click the VBoxGuestAdditions Disc Image File. VirtualBox extension pack: Oracle_VM_VirtualBox_Extension_Pack-6.1.10.vbox-extpack Note To remove the disk, right click on the disc icon and click Eject in the Ubuntu 16.04.2 image running in VirtualBox 5.1.14.

VirtualBox installation file name: VirtualBox-6.1.10-138449-OSX Host computer OS: MacOS HighSierra 10.13.6

Oracle vm virtualbox install guest additions ubuntu