When it comes to apps, one should use caution. This isn't just for writing apps, this the rule for any app will promise you the world, but many, especially the free ones, simply don't deliver. In fact, many do nothing. My suggestion to you is, read what they say it will do and then read the reviews. That will tell you if it is something you would use. A word of caution though, don't believe all the reviews you read since there are always sour grapes and those that don't like anything. I suggest you read all the reviews and look for common problems in each. In the end, you have to find what works for you.
When it comes to software, there is a lot out there, and depending on what you want to write depends on the software you need. Obviously, if you are simply writing letters, reports, or even magazine articles, all you need is a word processing program. For that matter, an old fashioned typewriter might suite your fancy. These are all items that do not require any specialized formatting or elements. If you are a writing a novel, you may wish to stick with the word processing; however, you have to work with what makes you happy. As for formatting software, the demented elves have one piece of advice: Test drive the different software using the demo programs before spending a penny. many are quite costly and it would be a shame to spend money only to find out it wasn't what you wanted. In regards to making any recommendations for software, the demented elves will not do so because each has something different to offer and it all is a matter of writer preference.
In the end, whether it is for learning to write or for formatting, one must find the apps and software that works for the individual. There is no one right way to do things (unless it is the format of the document itself). That said, remember buyers remorse can be painful so know what you are buying, even the free stuff. Just remember, there is no substitute for hard work, so there is no magic app (or software) that will write your story for you. Have fun with the programs, but put in the work.