Photo source: Wikipedia
Disregard the WI and WE characters, as they are now obsolete.
Can you see some similarities with Hiragana? The sounds are all the same, but even some characters look similar too. Aside from the similarities though, there are some things unique about Katakana.
Katakana's long sounds (long sounds are covered in an earlier post) don't use any a, i, u, e, or o. Instead, they use a stick, ー. For example, the word party is パーティー (paatii). To make a sound long, you simply have to put in a stick, that's it. I bet it's a major relief, considering that for Hiragana you have to remember that う is used for both long U and O sounds.
Now, I know it seems like I'm contradicting myself. I said before that Japanese people don't really have a sound for "ti" right? In Katakana however, yes, you can make this sound. You do this by writing テ (te) with a small イ (i). This combined creates the "ti" sound.
Similar to "ti," we can also create a "wi" sound (like the Nintendo Wii). We do this by combining ウ (U) with a small イ (I): ウィ. It's literally sounds like UI, but if you say it fast and combine both sounds, it begins to sound like (wi).
Katakana is strange, yes. But it's another alphabet for the Japanese language and is as crucial as Hiragana. As a student, you shouldn't complain about having to memorize more characters, because they are pretty easy to memorize if you study them! From my own personal experience, Hiragana and Katakana can be mastered in about a month each (or even less if you're really dedicated).
Begin studying and memorizing your Katakana!