Differences between # and . In CSS

Question

Hi guys, When i was reading and looking through some examples of css on sololearn, some program they use uses # and some . May i know the difference?

Eg:
.p{}
And
#body{}

Answer 1

n the CSS, a class selector is a name preceded by a full stop (“.”) and an ID selector is a name preceded by a hash character (“#”). The difference between an ID and a class is that an ID can be used to identify one element, whereas a class can be used to identify more than one.
http://www.htmldog.com/guides/css/intermediate/classid/