The Square payment app is used as a credit card
processing system that lets vendors charge credit cards through mobile devices or tablets. Square is the first mobile payment processor to be embedded in a smartphone, or tablet.
To use Square there is a flat rate of 2.75% for each transaction made. The fee is waived for transactions over $1,000. General Electric, Whole Foods, and Starbucks all use Square and many entrepreneurs prefer it as a digital payment option as well.