In "Brew Session" mode, the alcohol content is in the "Fermentation" mode. When you click Fermentation, the spaces in white are adjustable and reflect the actual measurements from the batch. The alcohol % (ABV) is calculated from the OG and FG measurements just above it. You can see that right above the OG and FG spaces it says "Recorded Actuals".
When you intially import a recipe into a Brew Session, it will take the OG from the recipe and "assume" an FG and calculate the resulting ABV. If you change any of the ingredients in the Session, the OG and FG under the Fermentation tab do not change because they are supposed to be recorded actuals. You can update them manually. You will notice that there isn't any place when formulating a Recipe to indicate FG or ABV.
When you are formulating a recipe, consider the OG primarily, and then if you are curious, you can use the ABV calculator to see what you will get if you hit your FG target, or you can manually manipulate the numbers under the Fermentation tab. The OG is the primary indicator of how "big" a beer is. Depending on the yeast you use and some other fermentation parameters, you will get various degrees of attenuation which will determine the FG and the subsequent ABV.
