I'm creating a game that uses user-generated blocks. But whenever I create my own block it always starts with “define”.
It looks like this:

define (if this sprite was clicked on)

How do I make this work?

Edit:It's on the forum list of blocks.So it must be intentional…

Under the define block, you must define your block.

Like this:

define bounce
change y by [10]
change size by [10]
wait [0.5] seconds
change y by [-10]
change size by [-10]

Then, you can scroll down to the “my blocks” section of the block palette, drag out the block, and use it!

The_Cool_Test_Alt wrote:

Under the define block, you must define your block.

Like this:

define bounce
change y by [10]
change size by [10]
wait [0.5] seconds
change y by [-10]
change size by [-10]

Then, you can scroll down to the “my blocks” section of the block palette, drag out the block, and use it!

Oh,so that's why it was already working when I pressed on the block.

The reason is simple.
If you create a new block, a

define example block (apple) 

will appear. Under it, you must put the code that this block means.
For example,

define example block (apple)
turn cw ((apple) * (2)) degrees
say (join (join [Yummy! I've eaten] (apple)) [apples today!]) for (2) secs

Then, every time you use that block in your code, Scratch runs the code that the block is supposed to do.
So, based on my example, every time you use:

example block (apple::custom) :: custom

it runs the code:

turn cw ((apple::custom) * (2)) degrees
say (join (join [Yummy! I've eaten] (apple::custom)) [apples today!]) for (2) secs