Hola, While I agree with aridilla that looking up in the dictionary is always the best way, I’d like to offer a shortcut here lest you go through the convoluted and tedious chunk of definitions in the actual dictionary. “Render useless” means: to cause to be or become; make: to render someone usepless. Ex. The news rendered her speechless. “render picture” means: to represent; depict, as in painting: to render a landscape, a picture. “Render” in this sense could also be a technical term used in computer science/graphics. It means: To convert (graphics) from a file into visual form, as on a video display. (like in Photoshop we render the photos.) Render have many more other meanings, I recommend you refer to dictionary.com for a comprehensive list of definitions.

Well, looks like it has several rather different meanings, some very concrete (such as plaster, to plaster a wall - enlucir) and some very abstract (such as give, generate, translate etc.). First of all, there is the verb "to render" and the noun "render". Each of them can mean a ton of things, see here explanations in English (including some related to your example "render picture"): http://www.wordreference.com/definition/render and a few translations in Spanish here: http://www.wordreference.com/es/translation.asp?tranword=render but I think the English definitions are more clear and extensive.