pls help

please help me, I'm going through a coding course but idk how to make this I have to make a program where you select multiple options from a checkbox but and those options will show up in a label but you have to click a button first, I already did that part but also it needs to separate the options with "," and "and" in the middle and "." at the end for example if you only choose 1 word it would be: milk. if it were 2 it would be: milk and cookies. and 3: milk, cookies and coffee please