Camisa AND camiseta for 'shirt'?

I was taking a Language and Culture lesson today. I have taken other Spanish courses/programs in the past and I have been told that the word 'camisa' means shirt. Today I come across 'camiseta' Are they both just as correct to use, do they refer to different kinds, or would you use them in different instances/situations? If they're both correct, why in the world do we need two words for shirt? Of course we have top and shirt in English...

I believe that camisa means shirt and camiseta meas T-shirt.

I believ that Robert is correct. Similarly, a big semi type truck is a camión, and a pickup truck is a camioneta. I don't know if these are actually diminutives, but I love the way the Spanish language modifies words in this way.

Right on, they are diminutives. There is a module on this in the Platinum course (19.6).
- hermano / hermanito
- abuela / abuelita
- café / cafecito
- cabeza / cabecita
- ...

I think you also see this in some names as well: Ana / Anita, Juan / Juanito, ...
 

I love how diminutives are applied to names in Spanish. The woman I Skype with in Spain told me her mother calls her "Adelita" though her given name is Adela. Last winter while in Cuba I visited the family of my friend Manuel who lives here in Roanoke. They told me they call him "Manuelito."

That's a perfect explanation! Thanks for the help, everyone:).