More cores let you do more things at once. Generally speaking, faster cores let you do single things faster. Currently provided by Intel, they range from the ultra-low-power Core i3 to the ultra-powerful quad-core Core i9 in high-end MacBook Pro and iMac to the Xeon workstation chips in the Mac Pro. The CPU - central processing unit - is the engine that makes your Mac go.
VPN Deals: Lifetime license for $16, monthly plans at $1 & more Mac upgrades: Are CPU upgrades worth it?