What key do I need to press to put in expontenial and logarithmic functions?

The natural logarithm function, denoted ln(x) has an inverse function called the exponential function, denoted e^x. That is what you call the antilog (I prefer the euphony of the exponential).
On calculators the two functions share the same physical key: One function is accessed directly and the other indirectly (SHIFT, 2nd F, or 2nd)
On the Casio FX-991ES the function ln and e key is the the one above the tan key.




The common logarithm or logarithm in base 10, denoted log(x) has an inverse function, the power function in base 10 or 10^x. In your terminology this would also be an antilogarithm.
The common log is accessed by pressing the log key to the left of the ln key, and the 10^x function is obtained with the sequence [SHIFT][log]



Note: The Input/output mode in the foregoing screen displays is the MathIO mode.

To calculate the natural antilogarithm (inverse logarithm ) of a number, press SHIFT [e^x] then enter the number and press =

The e^x function is the shifted function of the ln key.

For example, to calculate the inverse logarithm of 3, press SHIFT ln 3 =

To calculate the natural antilogarithm (inverse logarithm ) of a number, press SHIFT [e^x] then enter the number and press =

The e^x function is the shifted function of the ln key.

For example, to calculate the inverse logarithm of 3, press SHIFT ln 3 =

On scientific calculators there is a key marked [LN]. You use it to calculate the natural logarithm.
On older calculators you enter the number and press the key to get the logarithm. On newer calculators, you may have to press the key LN then enter a positive number to get its logarithm.
It is also possible (you do not say what model and make of calculator you have, so I cannot know) that the LN marking is not on a key but on the faceplate of the calculator (near a key). It that is the case you will have to press a key marked [SHIFT], [2nd F] or [2nd] before the function key.

The 12C does not have the common logarithm function built-in, but you can calculate it using the natural logarithm function (the blue g shift of the %T key, 2nd row, 3rd key).

The common logarithm of x is the natural logarithm of x divided by the natural logarithm of 10, or
log x = ln x / ln 10

Press 1 0 0 0 g [LN] 1 0 g [LN] /
and you'll get the result 3.

The 30XIIS does not have the capability of solving equations. It can, however, calculate expressions using logarithms. Use the LOG key for common logarithms and the LN key for natural logarithms. In both cases, press the function key, enter the value or expression, and then ) to match the ( the function automatically enters.

The LOG and LN keys are the second and third keys from the top in the leftmost column of the keyboard.

You have two keys [LN] and [LOG], the former to calculate the natural logarithms and the latter to calculate the logarithms in base 10. You press the appropriate function key then type in the value. No need to press the [=] sign.
In case you are wondering: these functions have inverses: the inverse function of [LN] is the exponential, accessed with the key sequence [SHIFT][LN]; the inverse function of the logarithm in base 10 is "raise to to a power", accessed with the key sequence [SHIFT][LOG].
I am enclosing a screen capture from the user's manual. It shows you several examples.

Use the log function (common logarithm). See screen capture for markings on key.

To evaluate the negative of a logarithm
Enter the number (argument) of the logarithm
Press the = key to have it calculated.
While result is still displayed, press the sign change key or (+/-).

Beware that -log(number) is not necessarily a negative value.

Another way to calculate -log is to use the relation
log(1/a)=-log(a) .

To use the log function you press the [LOG] key in the middle of the first row of keys.
To use it.
Enter the number the log of which you want to calculate (must be positive)
Press the [LOG] key
Result is displayed.

Ex log(33.54)
33.54 [LOG] result is 1.5255

Once a logarithm has been calculated, use the [+/-] key, the change sign key located between the [.] and the [=] keys, on the bottom row of keys. You must press the change sign after you have calculated the logarithm.

There are very few instances where you have two press two keys AT THE SAME TIME, the most notable of them is when you want to force the calculator into the BOOT SCREEN. Most key combinations are key sequences, meaning you press a key and THEN press another.

This said, let us get back to your question.

When you apply a function on an expression, then apply the inverse of the function on the result you get the original expression back.
If f is a function and f^-1 its inverse, by definition f^-1[f(x)]=f[f^-1(x)] =x
As you can see you do not need a calculator to find the result.

Concerning the logarithmic functions

For the natural logarithms (logarithms in base e) labeled [ln], the inverse of the logarithm is the exponential function e^
ln[e^(x)] =e^[ln(x)] =x

For the common logarithms (logarithms in base 10), labeled [log], the inverse function of the log is the raising 10 to the power of. It is usually called the antilogarithm or antilog.

y= log(x) is equivalent to x=10^(y)

Try the following exemple

log(14) = 1.146128036
10^(1.146128036) =14

To access the 10^x function you press [2nd][LOG]
To access the exponential function you press [2nd][LN]