Depends on your interests, on what you're already familiar with, what style you like to read.
I'd say that unless you have a specific interest or know basics then starting with a general introduction is just fine. There are multiple. Some examples are: Blackburn's Think, Russell's The Problems of Philosophy, or Nagel's What does it all mean?. The latter two only give an overview of what the authors are interested in while Blackburn tries a bit more to look at many field. Williamson fairly recently also tried his hand at an introduction in dialogue form with Tetralogue.
You could also start with an extensive history of philosophy. If so then don't take Russell's because it has bad interpretations of philosophers he doesn't like. Instead, take something like Kenny's A New History of Western Philosophy (beware: this one is like 1000 pages. But you could skim it and get the primary text when something is interesting).
Starting with primary texts can also be fine. Some require massive background. But other texts can be read without any background. Some examples that pretty much all philosophy students read are the start of Descartes' Meditations and Gettier's short paper. You could also start with one of the easier dialogues of Plato (Euthyphro, Apology, Crito, Phaedo). Something not that useful but short and nice to read would be Nagel's The Absurd.
As for resources on the internet, don't use wikipedia. Some articles are fine, but for philosophy in general it's sketchy. There are two encyclopaediae you can use instead: IEP and SEP. The latter is something that philosophers quote. It can get quite dense and hard to read at times (compared to, say, an introduction). The former is usually easier to read but not as good.