in order to write an exponential growth equation in the form y=a(b)^x, you first take the initial value and do what?

For an exponential growth equation of the form $y=a(b)x$, a is the yy-intercept and bb is the growth factor.
The initial value is typically when $x=0$. If the initial value you are given is when $x=0$, then you can plug in its value for aa in the equation.

This is because the y-intercept is when $x=0$. That is, plugging in $x=0$ into $y=a(b)x$ gives $y=ab0=a(1)=a$.
For example, if you are told a city has an initial population of 50,000, then you would plug in $a=50,000$ since $50,000=a(b)0$ gives $a=50,000$.
If the initial value given is not when $x=0$, then you need to plug its value in for yy and its corresponding value for xx into the equation.
For example, if you are given a city's population of 50,000 in 2001 but xx represents the number of years since 2000, then you would need to substitute $y=50,000$ and $x=1$ into the equation. This would give you the equation $50,000=ab$. To find aa, you would need to then write a second equation using a second given point or using the growth factor to find the value of bb if it is given.
If you were given a growth rate of 2%, then $b=100\mathrm{\%}+2\mathrm{\%}=102\mathrm{\%}=1.02$.

Substituting $b=1.02$ into $ab=50,000$ gives $a(1.02)=50,000$. You can then divide both sides by 1.02 to get $a\approx 49,020$.
If you were not given a growth rate but were given a second point, such as a population of 60,000 in the year 2002, then you could plug in $x=2$ and $y=60,000$ into $y=a(b)x$ to write a second equation. This would give you the equation $60,000=ab2$. You would then have the
system ${\displaystyle \{ab=50000,a{b}^2=60000\}}$ that you could then solve for aa and bb using the substitution method.