Quick questions about threads

I'm just getting into the concept of threading, i have a few questions to ensure i'm understanding it correctly. Am i right in thinking that a seperate thread will allow my game to use a seperate cpu core on the host computer, if it has one? And if i ran seven additional threads, i'd theoretically be able to fully utilize every core of an 8-core cpu ? Will stuff done in a seperate thread affect the main unity thread, if they're runnning on seperate cores? If i ran an infinite loop in a single frame for instance, the game would normally lock up, but if it's on a seperate thread will it just continue running away without affecting the main one? And also, will that apply on a singlecore system (if such things even exist nowadays)