Understand that Illustrator creates vector graphics and vector text. Vector graphics consist of lines and curves that contain mathematical objects called vectors. Know that Photoshop creates bitmapped graphics.
Bitmaps consist of tiny dots of color.
The eye fills in the spaces between the dots so the color appears to be solid. Realize that bitmap graphics are much larger in file size than vector graphics. Therefore, vector images take up much less storage space and can be downloaded faster. Understand that you can scale a vector graphic to any size without losing quality. A bitmap will change quality if you enlarge it or reduce it.