Overleaf (formerly WriteLaTeX) is a collaborative online LaTeX editor. Please don't use this tag for general LaTeX questions but only for those, where the use of Overleaf is relevant to the problem.
Where to find more
- Overleaf webpage (it also provides language specific sub-pages)
- Templates on Overleaf, which you can also re-use stand-alone
- Latex-tutorials, also e.g. on mathematics, figures and tables, references
However, please be aware that Overleaf also introduces some "simplifications" to code, i.e. it may compile fine on Overleaf, but may fail in your local setup.