Hi, good question! I'll try to explain about the basic grammar. に is used for the dirrection for places, for the purpose, for the indirect object Ex.) わたしはこうえんにいきます。(I go to the park.) わたしはさんぽにいきます。(I go to take a walk.) わたしはあなたにほんをあげます。(I give you the book.) を is used for the direct object. Ex.) わたしはにほんごをべんきょうします。(I study Japanese.) わたしはほんをよみます。(I read the book.) わたしはえいがをみます。(I watch the movie.) I hope this was helpful. To other Japanese people or advanced learners, please explain more if you can!

Ryoko's answer is great. Another point may be this: I was taught that with を、 think of it as a particle that shows something is being done to the object. Such as: ほん を よみます。 reading is being done to the book .

is にand を？Japanese is Agglutinative language，so，The particles is decrorate front words，for example，やまに のぼる I go to climb the mountain,やまis a place，にdecorate it，place に いく，go to where，it is simple，and another usage，Can be used in people，but it‘s difficult，be brief，whoに Verb，whenに verb. usage of を is modify verb，for example，I watch tv，わたしは tvを みる，nounをverb，do that thing.I hope that is easy to apprehend.

use this http://www.guidetojapanese.org/learn/grammar/verbparticles