Instead of thinking of the internet as this huge technical monster that will take years to understand, let's break it down to a simpler explanation.
Think of it as a regular everyday tube like a cardboard roll in a paper towel but a bunch of them are all different sizes. All the internet is trying to do when it is giving you that annoying loading sign is sending information from point A to point B. That YouTube video is trying to squeeze itself through that cardboard tube to get to you.
Now why is that tube not sending that 1 small video to your screen? It’s because that tube is not just for you, but it's for all the other devices on your network or in your house as well. So the 2 iPhones downloading the newest addicting game, a laptop trying to get homework submitted an hour before it’s due, and Moana playing on Netflix in the other room are all trying to get through that tube at the same time your video is.
So, with all those things coming in at once, it gets congested like traffic rush hour after work. Now this is where a wider tube is needed because the width of that tube is Bandwidth. With a larger bandwidth you don't feel that traffic even when you get home from work.
Let's say all those different things trying to come through that network were marbles. Each marble is a bit because this data is measured usually as bits per second or “bps”. Let's say you poured a bag of marbles in that cardboard tube slowly; about 10 marbles at a time. The marbles will all get through with ease with no errors and that's all your networks Throughput.
Now you used that same tube and pour 100 marbles at once. Plenty of marbles made it through but most overflowed out the side. The marbles that fell out of the side were errors in data while the ones that made it through are throughput.
Congrats, you now know the basics of Throughput vs. Bandwidth!