Can someone just tell me what this is and how do I do it again?

Hi, I was working on my piece a few weeks ago and accidentally pressed some buttons, I think. Anyway, this blue guide popped up at the side of the screen. It was quite a pleasant surprise-- made my life wayyy easier when writing and was all in all really nice. However, I couldn't figure out how to do it again and so when working on other pieces I couldn't bring it up. I've looked through the handbooks and all over the website but I can't find any mention of this, so if someone could please tell me what it is and how to apply it to my scores, that'd be great. Thanks!