The idea with TeX Symbols is simple. Write a Google Doc with escaped LaTeX symbols, run the add-on, and watch as it converts all of your code into the appropriate Unicode characters.
Step 1: write your LaTeX code in plain text.
Step 2: go the the Add-ons menu, select TeX Symbols, and click Replace all.
Step 3: enjoy as your LaTeX code is transformed into nice Unicode symbols.
If a symbol cannot be converted, it will be highlighted in red, and an alert will let you know how many conversions were unresolved. If you want to only convert a part of the document, simply highlight that region, and select the Replace selected option from the menu.
The difference between this add-on and other equation editors is that you can embed all of your LaTeX code directly into the document and convert it all at the end. There is no need to open up a separate editing interface or the Special characters menu every time you need to insert a non-ASCII symbol.
TeX Symbols is still a work in progress. Many symbols still remain unsupported, and I am testing all of them to make sure they are PDF-friendly. When the add-on is finished, I am hoping it might find its way to the add-ons store.