There is an order in which you are supposed to write each line in katakana. It's important that you remember this order when you start to learn kana. The stroke order is shown with numbers. The number 1 means it is the first stroke. Where the number is placed is where your pen begins that stroke.
The example below is the Katakana KA. You can see that it has 2 strokes.
The first stroke has a bend in it.
At the bottom you will see that the stroke ends with a flick.
The second stroke is a small downwards curve.