All functions begin with the TD.... The Parameter Info popup shows the names of the parameters in function calls. Google Sheets automatically shows a popup with all available method signatures within 1 second (1000 milliseconds).

Add-on menu
Interval button would generate the combo box with all available interval options.
The Technical Indicators button will load a dynamically updated list of indicators from the server.
Add-ons ➤ Twelve Data ➤ Update
Due to some limitations that Google Sheets imposes, e.g. Google Quotas, we provide the option to update the formulas manually and automatically. With this submenu, formulas can be updated manually in the selection, only the error ones, or all at the same.
Add-ons ➤ Twelve Data ➤ Settings
The first field allows you to change or remove the API key.
The second field accepts an integer number with the number of minutes for the automatic refresh of the sheet. Take note that the updates will only work when the Twelve Data Settings tab is open.
Functions
=TDStockList(symbol: string, exchange: string, country: string, type: string, headers: string)
=TDForexList(symbol: string, currency_base: string, currency_quote: string, headers: string)
=TDCryptoList(symbol: string, exchange: string, currency_base: string, currency_quote: string, headers: string)
=TDETFList(symbol: string, headers: string)
=TDIndicesList(symbol: string, country: string, headers: string)
=TDExchanges(type: string, name: string, code: string, country: string, headers: string)
=TDCryptoExchanges(symbol: string, country: string, headers: string)

=TDSymbolSearch(symbol: string, headers: string)
=TDTimeSeries(symbol: string, interval: string, exchange: string, country: string, type: string, outputsize: integer, order: string, timezone: string, start_date: string, end_date: string, prepost: string, headers: string)
=TDCurrencyTimeSeries(base: string, quote: string, interval: string, exchange: string, country: string, type: string, outputsize: integer, order: string, timezone: string, start_date: string, end_date: string, prepost: string, headers: string)
=TDExchangeRate(base: string, quote: string, headers: string)
=TDCurrencyConversion(base: string, quote: string, amountl: string, headers: string)
=TDQuote(symbol: string, interval: string, exchange: string, country: string, volume_time_period: integer, type: string, timezone: string, prepost: string, headers: string)
=TDPrice(symbol: string, exchange: string, country: string, type: string, prepost: string, headers: string)
=TDEOD(symbol: string, exchange: string, country: string, type: string, prepost: string, headers: string)
=TDTechnicalIndicator(name: string, parameters: string, symbol: string, interval: string, exchange: string, country: string, type: string, outputsize: integer, order: string, timezone: string, start_date: string, end_date: string, prepost: string, headers: string)
parameters might be a string consisting of customized parameters for the technical indicator as per documentation. Each parameter has to be separated by the ampersand (&) sign.