Computer science has lots invisible systems at work behind the scenes. These are the rules for how computer programs work, data is stored, and how devices will communicate over networks. One rule about computers and programming is the need to create systems that produce consistent results. The commands that make up algorithms must do that same thing every time. Data must be encoded that same way so that programs can process it. The ASCII chart is an example of one of these invisible systems, it is the set of rules for how letters and other characters are stored.
Lets start by looking at the example of a keyboard. When the A key is hit, there is not a tiny A that moves through the wire into the computer. Rather, that key is set to send an encoded version of A. It is represented by the number 65, in binary that's 1000001. So when the A button is hit, the keyboard sends a pre-determined set of electrical pulses that represent 1000001. On, off, off, off....etc. Picture a tiny flashlight flipping on and off. This happens so fast people are usually unaware of how much encoding is happening as they type.
For computers to be predictable this rule must always be true. A is always 1000001. This lets you type in a worksheet for students or a parent email, without needing to know the binary inside.
And this encoding is true for all computing devices. On a mobile phone, tablet, or in a spreadsheet, A is always 65, B is 66, and so on. This encoding is referred to as the ASCII chart. It assigned every character a number so they they can be encoded.
For students, they do not need to memorize the ASCII chart, rather they need to understand this underlying process of digitization. That computers can only store and process things that can be stored in binary. And, different information is encoded differently. The rules for the letters are not the same rules for a song, or for an MRI.
The point is not to memorize a particular encoding scheme, but to be aware that data and information is encoded, and there are different rules for this encoding.