You see your "images" the same way as you have seen images crop up in your everyday thinking. For example, if I ask you to think of your favourite shirt or the way the furniture is arranged in your home, certain images will start popping up in your mind.
Usually these images are brief, fleeting and not very detailed. For your creative visualisations, however, you'll want to hold the images for longer periods of time, and in greater detail, and with more clarity. The more you practice, the more vivid the images will be.
Note that although we use the word "visualisation", you are not limited to using visual images in your visualisations. You can (and should) incorporate sound, tactile sensations, smell, movement, emotions etc.
Note that many people are already visualising automatically in their everyday life, without necessarily knowing what they are doing. I used to play chess competitively - basically, every chessplayer is visualising moves on the chessboard, often many, many moves ahead. Artists are already visualising before they start painting. Architects probably do that too. If you drive, you probably do it too, as you work out what is the shortest route from Point A to Point B. Actually, many people are probably visualising as they do mental calculations such as 372 divided by 4. Etc.
People with very strong capabilities of visualisation linked to memory are referred to as people with "photographic memory".