The final thing to do with Siril is to stack the images. Go to the "stacking" tab, indicate if you want to stack all images, only selected images or the best images regarding the value of FWHM previously computed. Then simply click on "Sum Stacking" which is the regular stack. The Median Stacking is mostly used to create pre-processing frames, like offsets or darks and Pixel Maximum Stacking is very usefull for star trail pictures.