Linking File Standards--Spreadsheet files can be integrated into QGIS files by simple drag and drop--however certain standards are applicable. Only the top row of the file can be used for column titles. The column titles must be in text mode or QGIS will not recognize them--for example if you are loading time series data, make sure all of the time/date data is in text mode--to change a number like 2010 to text simply insert a leading ' as in '2010. If the file contains a list of countries make sure that the 3 character ISO code is included as one of the data columns to ensure easy linking to the list of countries in the attribute file (for more information on ISO codes see Table Format
Editing the Attribute File--
The attribute file can be edited within QGIS. However, if for some reason it is more convenient to edit it outside of the GIS software using LibreOffice Calc than Excel--The attribute file is in dbf format and LibreOffice Calc supports dbf while Excel does not.
Longitude and Latitude--
If the file you are linking includes columns for longitude and latitude, the column headings longitude and latitude must be fully spelled out to be recognized by the system.