Thank you for questions like this. It opens my eyes to how deceptively difficult Bahasa Indonesia is to non-native and how I as a native speaker take it for granted. When I learned english many moons ago, I found out quickly how important articles are in that language and my inofficial mentor (husband, native speaker) teased me because I put 'the' and 'a/an' in all the wrong places.. I still sometimes forget to use either. For Indonesians, articles aren't particularly important unless you are trying to put an emphasis on a certain subject. In your example above, you want to put 'itu' after 'pria' because you are not talking about any man in general. In the formal indonesian, we use 'tersebut' as in 'pria tersebut' or, in english you use 'said man' - if that helps to clarify the difference of the view and use of articles from both languages. Same thing with using seekor ayam as opposed to just ayam. The use of 'seekor' emphasizes that there is only one chicken in particular instead of referring to chicken in general like .kucingku suka mengejar ayam' (my cat likes to chase chickens). On another note... .Itu' can stand for verb is/are, like 'Bobby itu teman saya' (Bobby is my friend) - rarely/never do native Indonesia speakers use 'adalah' which is the direct translation of is/are.