You use the with an uncount noun when you are talking about a particular example of that thing. You use the with count nouns the second and subsequent times you use the noun, or when the listener already knows what you are referring to (maybe because there is only one of that thing). See this article. It explains it best. http://esl.fis.edu/grammar/rules/article.htm

Here's another way to think about it, what we are taught as kids. These aren't official definitions, but they're much easier to understand. 'A' and 'an' just mean 'one'. I have a cat = I have one cat. A window is over there = One window is over there. The difference is that you can only use 'a' and 'an' before a noun and that it (or 'the') is compulsory when talking about one of something. 'The' is used when the person already knows how many or how much of the stuff there is. I have one cat, one cat is very cute = I have a cat, the cat is very cute. There are eight chairs in one room, eight chairs are made of wood = There are eight chairs in the room, the chairs are made of wood. One bottle has two litres of water, two litres of water is very wet = The bottle has two litres of water, the water is very wet. Actually in those last examples, those sentences aren't necessarily equivalent. For example, in the sentence "I have one cat, one cat is very fat" the cat that is fat could or could not be my cat, it could also be any other cat. "I have one cat, the cat is very fat" indicates that the cat that is fat can ONLY be the cat that was already quantified ie. my cat. Hope this helped.

If you have specific subject or substance , you may use "THE" for instance, I like THE accommodation, but i need food to eat THE accommodation which i have reserved , it is a specific noun food is non specific , so I do not use the food