Zend certified PHP/Magento developer

Cant understand visually what main memory is

According to my university’s notes the main memory is made of a consecutive number of positions, each of them contains the same amount of binary digits. Every position corresponds to a unique address which is what the CPU uses as reference to load from the memory. However I can’t visualize this. Is the main memory some form of a grid, in which each cell has a unique address and that is what the CPU uses as reference to load data from it?