I feel a bit ignorant about this question. However, it seems urgent to me:
I often come across code examples when searching for something like 
https://gis.stackexchange.com/questions/30493/geotiff-size-what-to-do#30496. Sometimes, the presented code examples seem to do exactly what I was searching for. There is just one big drawback: I just don't know which type of console is to be used. 

In the example, you findit says:

"you may try out something like the following, using the GDAL utilities:

    gdal_translate -co "TILED=YES" -co "COMPRESS=JPEG" -co "PHOTOMETRIC=YCBCR" input.tiff output.tiff
    
    gdaladdo -r average --config COMPRESS_OVERVIEW JPEG --config PHOTOMETRIC_OVERVIEW YCBCR output
"

So I googled GDAL utilities, but that didn't help. I am used to R, but apart from that, I am quite unfamiliar with coding. I hope someone can indicate which program to use/what to do with such code examples.