LyX is an open source GUI developed to make it easier to use LaTeX without learning the codes.
TeX, a typesetting language invented by Donald Knuth in 1978, was enhanced in 1982 when Leslie Lamport developed LaTeX as a platform to use TeX. Over the years LaTeX acquired many convenient features and became the standard tool for professional document processor for math.
By using LyX, you get the benefits of using LaTeX without the pain. You can type complicated math equations, properly format definitions, proofs and lemmas without learning code. It provides cross-referencing within the document, automatic numbering of sections, footnotes and references.
Find the latest version of LyX and all resources from The Official LyX Site.
Official Help Documents: You can find detailed help within the LyX, under the TOOLS menu. There is a tutorial with a sample document you can use to practice on, using the tutorial that gives instructions. A User Guide is available also.
Third Party Help: Just look up things you are having problems with using a search engine. Make sure you have up-to-date instructions by filtering results by publication date.
In Google, that means once you have the results page, use the Search Tools button > choose your timeframe from the Any Time dropdown list > past year (for example)