This character 缶 is rarely used in Chinese. The meaning of this radical is borrowed from Japanese: 缶 (=かん) = box. It is understood as a pestle 午 in a mortar 凵. As the pestle 午 in the mortar is vertical, it has the meaning “noon” [wǔ], as the sun is then also vertical.
Tip: Go to the radicals that are contained in this character and learn all the characters with this radical systematically!
The app has many other functions, such as character selection according to difficulty, practice programs, handwriting recognition and success statistics!