An Expert Advisor template is a file designed for writing a source code. After it has been created, it is automatically placed in MQL5/Libraries (or MQL4/Libraries) directory.
After choosing the corresponding position in the MQL4/MQL5 Wizard and pressing the "Next" button the following window appears:
The following fields should be filled out in this window:
Once all the necessary fields are filled out, the "Done" button will become active. As soon as it is pressed, the project of the library will be created and the window for writing its source code will be opened automatically.