Enter the amount used of each fuel type in the relevant unit

There are 4 different ways that you can fill in the fuel types by mass (tonnes) or volume (litres) and then by net or gross calorific value.
If you are billed in kWh then you must either put the data in as net or gross calorific value. If this is not clear from your bill then you must contact the supplier to find out which it is. Failing to do this will lead to inaccurate results.

Just add the fuel used into the relevant cell of the relevant table. If you have some fuels measured in litres and some in tonnes then its fine to put some in each table. Similarly if halfway through the year the way your fuel was measured changes then just put half in each table. As long as there is no repetition of data this is not a problem.