01:00 - Aridity index + Evapotraspiration formulas
02:50 - Downloading Bioclimatic variables 
03:20 - Spatial resolution of pixels in minutes and seconds - which to download?
09:00 - process toolbox ... what to do if there is no processing toolbox in our QGIS?
12:30 - PREDEFINED EXPRESSIONS - code your formula in a predefined expression
13:45 - Naming your variables for your predifined expression
15:40 - Raster calculator using the reference layer and customized extension over our study region
19:25 - Evapotraspiration and Precipitation to calculate Aridity