That actually is a pretty good question. After shutting down your computer, it is normal for the amount of free RAM and the size of VM to change. Basically RAM is where temporary information like user settings and application processes are stored but are not written to the hard drive. This allows for faster access to this information than having to read it off of your hard drive. When you shut your computer down anything that is stored in RAM is erased, that's why it changes.
Now for VM, lets say you have 4GB of physical RAM, and you start using a bunch of different applications, and you use up all of that. Now your computer starts using your Virtual Memory, which is space that is allocated on your hard drive, that acts just like physical RAM, but only exists temporarily. This allows your computer to exceed the size limit of your physical RAM. Since it is stored on your hard drive, accessing Virtual Memory is slower than accessing your physical RAM.