In Japan it is considered extremely rude to call somebody’s name, first name or last name, without an honorific title (suffix) afterwards. Not using any suffix is called 呼び捨て（よびすて） in Japanese and it is not the done thing!
The easiest and the most common suffix is “-san” and you can use it for almost anybody, whether you are calling their first name or last name. (BTW, when Japanese people are speaking in Japanese, they say their family name first and then their given name. They don’t officially have middle names in Japan, though those who have multiple nationalities may have their middle names recorded in their Japanese passport in brackets.)
In the service industry, customers are usually called with the suffix of “-sama.” Teachers and doctors are called with the suffix of “-sensei.” Little children will be called with “-chan” as their suffix.
One thing you should remember is that you should NOT use any suffix to yourself or members of your own family. Putting “-san” to your own name sounds very immature or arrogant.
Another time you don’t use any suffix is when you are calling people by their nicknames. So if you make a Japanese friend and if his/her nickname happens to be the same as his/her first name or last name, you do not need to use “-san” with that. The best way is to ask your friend what he/she prefers to be called!