With regard to memory, it's commonly believed that we can hold 7-8 pieces of information in our working memory, but it's actually 3-4 chunks of information.
Chunking is when you organise information into smaller meaningful chunks to make them more manageable. This works best in groups of threes or fours and is usually the way we remember phone numbers: 012-345-6789
Imagine that your short-term memory is like writing on a foggy mirror.
You can write small words or pictures on it, but after a few moments, the writing fades - just like the memory. You can extend how long a short-term memory lasts by repeating it in your head or out loud. It's kind of like writing on the window once the original writing has faded.
Each time the information is repeated; it re-enters the memory cycle and will be forgotten in 15 seconds or so.
Short-term memory IS different to working memory, though the two are often confused. Working memory represents the ability to process and manipulate information that is held in your short-term memory. An example of working memory is when you're engaging in mental math, holding numbers in your head while manipulating others and then performing further calculations on the initial results.
Hope this helps!