so when you're editing your profile, you can put HTML tags in any of the text boxes alongside plain text. there's a list of allowed HTML elements on the left side of the edit page. for styling, any CSS contained in <style> tags will be applied. I would recommend keeping all your CSS in one text box (I use "about me" since it's at the top).
how much do you know about HTML and CSS? if you don't know a lot, in my opinion the best way to learn is by thinking of a specific thing you want to do (example: change the background of this element to red, change the text size somewhere, etc) and searching for how it's done. stack overflow, mozilla developer network, w3schools, css-tricks are good websites for info.
as you keep trying new things you'll start to pick up on everything and build your knowledge. messing with your spacehey page is a great way to start learning since it's less involved than writing your own website from scratch.