Express 2/3 as a decimal or 0.6 as a fraction. 2/3 as a decimal is 0.666... which is bigger than 0.6.
0.6 as a fraction is 6/10 or 3/5. Compare 3/5 and 2/3 by expressing each as a fraction with the same denominator: 3/5 is 9/15 and 2/3 is 10/15. 10 is bigger than 9 so 2/3 is bigger than 0.6.