I want to have something written in the top-left corner and top-right corners of my document. So I want some text aligned to the right, some to the left, at the same height. I could do it with spamming the space bar, but then if I change the font size or anything it will be broken again. Is there any way to do this more neatly?
In the ruler above your document, click where you want the right-most character to be. Then select the option that pops up: "Add right tab-stop".
Then, on that line, type your left-most text as normal, then hit the Tab key until your cursor is located at the tab-stop you just created and type your text. You should notice that it fills in from the right. Now you shouldn't have issues when you change your font.
If the ruler is not appearing above your document, make sure you have
(More at Page setup)