The Particle o, ni and e

Sorry but I mix up these to particles "e" and "o", before I mixed up "e" and "ni" but then a teacher explained to me that "ni" is for direction and "e" is... something else, I guess I need to work on it.

"o" is used as at?

"sakana o tabemasu." sorry if i am wrong but I don't see the use for the o particle therefore I don't really know when to use it if I were to make a sentence.

as for the "e" particle, how is it used? if it means at as well but not direction, how can I use it?

p.s. does the particle "ni" have to do with the words "hajini" as "haji" means first what does ni do? same goes for "hontoni" as "honto" means really.

を (pronounced お) is the direct object marker.

http://en.wikipedia.org/wiki/Object_%28grammar%29

Putting it after a word is equivalent to declining that word in the accusative case in languages which decline, such as Latin or German. It's normal that you don't see the point of having it since it has no equivalent in English, where the verb and its direct object are simply juxtaposed (the same happens in French also). You will have to get used to it. In colloquial Japanese, it is sometimes omitted, but this would not be considered correct in a formal setting.

へ (pronounced え) indicates direction of movement. 「東京へ行きます。」

に has many, many different uses. In particular, it can replace へ as the direction marker in some cases, when the direction is not a place in the proper sense, but something more abstract. 「買い物に行きます。」

You can use both に and へ for direction. The difference is that へ is used simply to indicate the direction, while に is more specific and often with a certain purpose/reason.

学校へ行く Go to school (school as the destination of one's movement. One physically moves to(or towards) a school.)
学校に行く Go to school (to study as a student, for instance.)

p.s. does the particle "ni" have to do with the words "hajini" as "haji" means first what does ni do? same goes for "hontoni" as "honto" means really.

In this case, ni is used to change a na adjective into an adverb. Hajime ni (not haji ni) means firstly/ first of all, and will generally be used with a verb. Hontou means real or true, so hontou ni means really or truely.

I see, "ni" is used for the place and it's action, and "e" is the place itself, Thank you all, I totally understand now, as for the "o" particle, I might get that for a while.