These two words have different meanings. 1. 'Last' means final, except when it's in combination with a time period, in which case it means the one before this one. eg December is the last month of the year = the final month I went to Spain last year = the year before this one 2. 'Latest' is the superlative form of the adjective late. eg I need the report by Friday at the latest. 'Latest' can also mean 'most recent'. eg Have you heard this band's latest album?

As always, it depends on the context so when asking specific questions like these, you should give us an example. Otherwise you are asking us to come up with every possible answer, which is a lot of work and it's often unnecessary. To try to answer your question, usually either can be used. The main difference in their meaning is that "last" refers to something that there is no more of whereas "latest" has a conotation of more to come. You could also say that "last" may refer to the one at the end of something (a list, aisles, rooms) whereas "latest" has to do with time, like the latest issue of a magazine. Hope this helps, otherwise (and for the future) please give examples.