How do I import existing Virtual infrastructure such as VM's into my Terraform state file?

I can not figure out how to import existing VM’s into Terraform so I can manage them and eventually destroy them all at once. I have a main.tf, variables.tf, and a terraform.tfvars files. These allow me to create servers and assign static mac’s, etc… but when I try to import existing infrastructure it does not work. I also get a tainted version of the vm. I must note I am very new to this.