There are also Settings, which already have descriptions in the Setting's menu.
Bar at the top of the window, has buttons for saving/loading saves and other basic function and displayed data.

Lists all saves in localStorage (more info on home page). There is a "Load" button next to each listed save, this will load and overwrite whatever is currently loaded.
The "Remove" button will prompt the user for confirmation, and (if granted) will delete the save from localStorage.

Prompts the user for a save name. When submitted, this will save to localStorage as "SatisfactoryCalc - Save:{name}".
If the same name as another save is submitted the user will be prompted if the save should be overwritten, and (if granted) will overwrite the save in localStorage.
Save or Download often.

Prompts the user for a JSON file. When submitted (if the file is processed successfully), this will load and overwrite whatever is currently loaded.
Note that this is done client side, this file is not sent to an external server.

Generates a blob link to a JSON file download of what is currently loaded.
Saving the JSONs locally is a good way to ensure you do not lose your saves.

Lists templates to start off from. There is a "Load" button next to each listed save, this will load and overwrite whatever is currently loaded.
Ensure to read the note that is shown when loaded.

Settings that change how the calculator works and looks.
Saved into localStorage.

Submit button, calculates and renders everything.
Shows calculation status. 🖌️ = Rendering, 🔄 = Calculating, ✅ = Done.
The toolbar also shows the values: % complete, total MW consumption (average), and total awesome points produced.
Section for editing item data and setting input demand.
Forms at the bottom to edit/add items and categories.
Customizable item category.
Uses HTML element ID for selection, so non alphanumeric characters (except spaces, which are replaced by "_") may cause issues.
Customizable item name (used as a unique identifier).
Uses HTML element ID for selection, so non alphanumeric characters (except spaces, which are replaced by "_") may cause issues.
Individual item calculation status. Most useful for debug to see where calculation fails.
Used to mark an item as complete. And calculate % complete.
One can change if items with 0 total demand count in settings. There are also check/uncheck all as complete buttons.
User input-ed demand for each item.
Sum of Calculated Demand - Byproduct (When reuse bypro setting is true).
Demand from calculation.
If Calc. > 0: | Calc. |, else: 0. (When reuse bypro setting is true)
Total demand.
Inp. Demand + Calc. Demand
Byproducts.
If Calc. < 0: | Calc. |, else: 0. (When reuse bypro setting is true)
Maximum clock speed allowed for buildings. Maximum specifically because the remainder building's clock speed will be set so that item demand is matched exactly.
Taken as a percent (100% = 1 or a normal clocked building).
Somersloop Multiplication value. Multiplies output, such that a fraction of the recipe's input items are needed. This field accepts any number, and may not reflect what is possible in satisfactory.
Total amount of buildings needed to produce the demanded amount of items. Fractional portion represents the clock speed of the remainder building.
Drop down menu. Select whatever recipe desired.
Average, Maximum, and Minimum MW usage needed to produce item.
Awesome points per item.
Awesome points per minute given input demand.
Awe. Pts. Key * Inp. Demand
Awesome points per minute given byproduct.
Awe. Pts. Key * Bypro.
Displays all the recipes. Similar category/item organization as Main Interface.
Form at bottom to edit/add recipes.
Has a building table and an awesome points table.
Form at bottom to edit/add buildings.
Total whole number of buildings required (by type).
Average, Maximum, and Minimum power used by a normal individual building type.
Average, Maximum, and Minimum total power used by each building type.
Uses a complex formula that can be edited in settings (more details in settings).
Shows Awesome Points per minute from Input Demand and Byproducts, and their sum (Total).
Table that shows each item (output, horizontal), and how much of each other item (input/bypro, vertical) that item requires/produces as byproduct.