Here - again - we do have a sound that is the same and has two different ways of being written. It's actually nothing special just a simple s like in song or sauce. But as everything German language has a history that makes this actually redundant, but since we like tradition we keep it.

Er hieß His name was.   weiß   white

Then there is the orthographic rule when to use which one of those. Actually you don't have to worry about it for quite a long time. Since everyone will understand, if you say that this letter is not on your keyboard so you always can substitute it with two ss. Just that you know, that there is a rule (after long vowels and diphthongs is ß, after short vowels the ss).