Compound interest means that interest is charged not only on the principal, but also on the calculated interest.

Therefore, one year after the principal p, the final value f should be:

F 1 = px (1+I) = p+Pi, where p is the principal and Pi is the interest of the first year. You can understand this, right?

In another year, interest should be calculated not only according to the principal p, but also according to the interest Pi of the previous year. therefore

f2=f 1x( 1+i)=px( 1+i)x( 1+i)=px( 1+i)^2。 You can learn about it here. Is it because you missed the power sign here that you don't understand?

In another year, F3 = px (1+I) x (1+I) x (1+I) = px (1+I) 3.

3 represents the third power of the result in front brackets. Do you understand now?