Anytime you take on any endevour you should have some preliminary research done. NPK is one of the most basic and absolute concepts one needs to know even at the most amatuer levels. N-P-K is a ratio of the three most essential nutients all plants need to sustain life. Nitrogen-Phosphorous-Potasium(K can be a confusing connection to make, but you cant have two P's). Get a book or you'll rely on this site way to heavily and be held up in your endeavor. And yes, soil contains enough nutes for 2-4 weeks generally speaking. Don't get dicouraged, just give more of your own intiative to obtain some basic knowledge on your own. This site is very helpful and many members give alot of their time to help eachother out.

Peace,
Snow Owl