Download speed is actually talking about your bandwidth, specifically your downstream – the part of your connection that receives data from the internet.
Instead of making data move faster, a higher bandwidth (what is listed as higher ‘download speed’) means more data can move through the connection at the same time.
The download speed is the maximum amount of data that can be sent to your connection, so a 17Mbps ‘speed’ means you can receive a maximum of 17 megabits of data every second.
Similarly, if you have fibre broadband capable of ‘up to 76Mbps’, that means you can receive a maximum of 76 megabits of data every second.
Your ‘download speed’ is relevant for almost all online activity as everything you see on the internet has to be sent to you through the downstream.
A higher ‘download speed’ increases the maximum potential of your broadband, but it doesn’t guarantee that every task you do online will be any quicker.