There is really not so much to learn. What you need to do is learn it layer upon layer.
Start off like this: EVERY profile needs to have the following three headings, and this is how you write them on the Edit tab:
where you write the person's life story
where you put the sources that back up the dates, places etc
where you list things/people which have been useful, but aren't sources
You list the sources under the ==Sources== heading (with <references/> immediately underneath), using bullet points (there are other ways, but just stick with bullet points for now):
* Here is a source
* Here is another source
* Here is yet another source
And that's it! When you have these under your belt, you can start learning about internal links, inline sourcing, adding images and so on.
How to write sources: I recommend you get them from FamilySearch.org, who have actually got a little section 'Citing this Source' and it's all written out for you. If you already have them (and it sounds like you have), just write them down, preferably so someone else could find them if they wanted to. If there's a link, use it. If there isn't, don't. Here are some made-up examples:
* UK birth registration: Stow, Volume 5b, Page 33, March quarter 1844, mother's maiden name PHILLIPS
* 1878 Land Grant to Fred Doe, Courthouse, Gorham, Maine, USA, viewed online at [link], hardcopy in possession of Norma Gehring
* 1898 Last Will and Testament of Fred Doe held in possession of Norma Gehring, National Archives ref DD1/1234 WT/2
Hope that's helpful.