Any rule(s) about combining nouns with other words to form new nouns? I came across the sentence "行进路线上的生物早早就避开了" and I interpret "行进路线" to mean marching path. 行进 means marching/advancing and 路线 means route/path so marching path seems to make sense, but this is my first time seeing this manner of speech. Are you generally allowed to combine a verb and a noun together to form a new noun or is this a special case?

Edit: I just came across another example, "骷髅兵". Skeleton + Solider... .so... skeleton soldier? Is it truly that simple? This is how it works in English but I don't expect such a behavior to carry into Chinese. I apologize if this is a very noobie question but I'm just now encountering this.
Of course you can. It's much simpler in Chinese actually, because the etymology of Chinese words is pure Chinese, instead of various languages like of English words.

Yes, you need to know that "word" is not a clear concept in Chinese. Basically, a sentence is composed of character combinations, among which some combinations (sometimes just a character by itself) are frequently used or have clear definition (e.g. scientific terms) thus regarded as words. What I want to say is that whenever the combination is meaningful, you are fine to use it.

And interestingly, this feature contributes to the extensive phenomenon that a combination of characters (word if you want) can be read as different things according to  its context.

E.g.

如临深渊，相机行事。
（像在深潭边走路一样谨慎，观察时机灵活办事）

买了一台新相机
（照相的机器）

未详其实，不敢妄言。
（没有清楚地知道那个事实，不敢随便发表议论）

其实他昨天没有回来。
（确实，作连词）

生啖鹿肉，颜色不变
（生吃鹿肉，面容表情不改变）

冷暖彰益，颜色调和。
（冷色和暖色相配凸现各自的好处，多种色彩和谐相容）

木石错置，纷呈杂然。
（树木山石交错设置，混杂地纷纷展现）

错置于此，其得宜乎？
（安排（措置）在这里，难道合适吗？）