"Juma is the name of the Tanzanian."
Translation:Juma ni jina la Mtanzania.
La is essentially just "of" whereas forms like langu (my) and lake also include mention of the owner. La has to come before another noun.
jina langu = my name
jina lake = her/his name
jina la ... = the name of ...
Of course, the forms with l are just one of the possibilities. There are a few examples plus a table of all the forms here: https://en.wiktionary.org/wiki/a#Swahili