What is the difference between var and let/const?

Var has functional scope, while let and const have block scope. Block scope meaning they are only able to be used within the block of code (denoted between {} ) they are declared in. Additionally, const is not able to be overwritten, but it is mutable.

What components are needed for a computer to work, as well as software?

Motherboard, power box, processor, RAM, graphics card (whether internal or external), something to display it on, keyboard OR mouse, an operating system (OS).

What would happen if there was no more friction in the world?

Walking would be impossible, as a mater of fact everything would feel like the slipperiest soap available, and be near impossible to grab things unless you completely encircled them. Cars and any other machine would cease to function correctly, and anything on an incline would immediately start sliding off. The slightest touch would send things flying forever until they hit something else. All in all, it would be very strange indeed.