RAM is what is also called the memory in your computer. RAM is Random Access Memory
The RAM is where the computer puts things it is current working on. It is like in your brain the things you are currently thinking about. It is a temporary location where things are on the computer. When the power is turned off to the computer everything that is in RAM is gone. You could put your computer in hibernation or sleep mode and stuff will be remembered but that is because when you go in these modes everything in RAM is written to the hard disk. Basically, RAM is similar to your memory in that when you die no one will ever know what you had stored in brain or were thinking about.
Today RAM or memory is measured in gigabytes or billions of bytes of memory vs your hard drives today are usually in terabytes or trillions of bytes of storage. A byte is essentially the space it takes to hold one character that humans are used to such as a letter or number. Usually if you are buying a computer now you want at least 2 gigabytes of memory for basic use or 8-24 gigabytes for more advanced uses.
There is permanent memory on a computer also that is called ROM (or words ended in that) that is where the information is stored that tells a computer how to start. ROM stands for Read Only Memory and the contents there are written when it is manufactured and cannot be changed or deleted.