Hi, first activate the Stock Ticker option on Settings > Google News > Advanced. Then, edit the post where you wish to apply a stock ticker to and find on the right side (normally below Tags) the section Stock tickers. Add the stock as you would add a tag: type the code and hit Enter to create a new stock or select any proposed existing stock ticker. Use a comma to add multiple stocks.
A stock ticker must be prefixed by the name of its stock exchange, and must match its entry in Google Finance. For example: NASDAQ:TSLA would correspond with https://www.google.com/finance/quote/TSLA:NASDAQ (notice the search field at the top in contrast with the URL path)