A favicon is a file that contains one or more icons for a website. If you wish you can read more about favicons on Wikipedia.
There are nine different sizes of favicons that are a currently recommended (2020), (16, 32, 96, 120, 128, 152, 167, 180, 196).
These consist of four Apple Touch icons, one Android and four browser icons.
If you upload the largest, 196, to the right place then UDB will create the other sizes and the links to them all.
Favicons are heavily cached and the session will need to be updated so you will probably need to completely exit the browser and re-open to see the changes.