I am the first intern in the company. I was tasked to create an internship manual as my legacy. I want to make a creative one and instead of using a word, I want to use a layout and designing tool. I'm a student so I am looking for a free one for my mac.
For something like this you would probably be looking at a program close to Adobe InDesign. InDesign isn't free and is one of the more expensive products Adobe offers, but would be the ideal tool for the job.
If you look at Scribus as a free alternative to InDesign it might be what you're looking for. There is a bit of a learning curve and isn't all that intuitive but does give you more options than Word.
Also LucidPress might be an option to look into. It's a web based program and I haven't used it so can't vouch for how good it is but it seems popular.
If you have the most recent version of Microsoft Office try using Presentation. It is very basic but can be a bit better to use in terms of layout than Word is.
Ideally InDesign is the best, but these options do give you a bit more functionality for this than Word offers for free.
The main options for you will be Scribus or TeX. Depending on the type of manual TeX would probably be a better option.
Scribus is a free opensource WYSIWYG desktop publishing application.
TeX will seem more complicated, and it is, but its also incredibly powerful for Desktop Publishing and specifically typesetting. If your internship is at all scientific or mathematical in nature you'll probably be better off learning TeX. There's also an entire StackExchange community for it: TeX.stackexchange.com that can help you out.