Eqyation problem

[alireza1998]

Hello .
How do I enter the following formula into the equation section?
pop(t)=pop(t-1)+popg
pop means population
popg means population growth
t is current year , t-1 means last year

[Administrator]

You need to use a level.

Have you gone through any of the tutorials yet?

[alireza1998]

You need to use a level.

Have you gone through any of the tutorials yet?

I create level (population) , flow (population growth) , constant (population growth rate)
for equation of population i have to use this (population(t)=population(t-1)+population growth
But I don't know how to introduce t and t-1 to the software?
I think t is the current year and t-1 means the previous year