Resolution

 

        The difference between 300ppi and 72 PPI is the quality. The higher the PPI the better the image looks because of its greater pixel density, Smaller pixels allow for a smother blend of color and shape which is another reason 300PPI looks better than 72 PPI. Resizing the image wont change the dimensions or size but it will change the printer outcome. A 300PPI image will be printed at a smaller size compared to the same image on 72PPI. Exporting your design in 300PPI is better for a more professional quality look, while 72PPI is better for a website image. 

PPI is pixels per inch 

which is the fixed number of pixels that a screen can display and the density of pixels within a digital image 

DPI is dots per inch 

is commonly used in printers to spit out tiny dots and create images