Er es and Sie.
I have a question. So Er is normally used as a synonym of he, es-it and sie-her. However I've noticed in my studies that often in inanimate objects that have no gender are sometimes called er or sie. Is this something I just have to learn like each words die, der and das? Does it have something to do with the 'the' of the work? eg. der Aunzug would be Er?
The idea of gendered nouns have nothing to do with gender. Das Mädchen means girl yet is netur not feminine. So with animals no matter what the gender of an animal is it will always take the grammatical gender, for example my female dog will still be Er because it is Der Hund. So to answer your question it would be sie lauft
er = he sie = she (not her, her would be "ihr" in German) es = it
Der, Die, Das are the three definite articles (like "the" in English, "la" and "le" in French and so on).
If I understood your question correctly you wanted to know why you can refer to an inanimated object with "no gender" as Er, Sie or Es, right?
First of all, EVERY noun has a specific grammatical gender.
Der Anzug (m) - the suit Die Arbeit (f) - the work Das Kleid (n) - the dress
We don't often refer to objects as er, sie, es, that was the reason why I had to think a really long time to find a proper example, but I've found one.
Q:"Wie war dein Tag?" (how was your day) A:"Er war furchtbar" (it was terrible)
But even in that situation a native speaker would just say "Furchtbar" not "Er war furchtbar"
For example :
Wo ist der Anzug? (Where's the suit)
You can answer with :
Der Anzug ist im Schrank. (The suit is in the closet)
Der ist im Schrank
You can also say:
Er ist im Schrank
But be aware that it is clear what you're talking about, because everybody would think there is a person in the closet.
If you want to use : Der ist im Schrank. Die ist schön.
Be aware that the object you're referring to has already been mentioned in some way within the conversation before