I’m an absolute beginner at Latin pronouns, and so I’m scared of falling into trap and messing up my Latin, so I’d like a good clarification if possible. 
Okay, my dictionary lists both “is/ea/id” and “ille/illa/illud” as “he, she, it”. I tried looking up the differences, and one explanation was that the latter set made a previous “object” into a subject. Honestly, that’s not a lot to go by, and I’m absolutely unsure about the cases where “ille/illa/illud” modify things as “that” (and possibly like a definite article?)
Are there any simple rules that govern the way to use these words? (I’m sure there is!) On a side note, I’m also interested in the use of pronouns in Latin in general. Does the language depend heavily on them, or (like say one of it’s decendants, Spanish) hardly use them as subjects at all?
Any concise and right to the point explanations would be greatly appreciated. Thanks in advance. 