The numbers in the for block work as you probably think they do: the inner script is run enough times to count from the left number (1) to the right number (10). As with the repeat block, you can change the numbers it comes with by default to change the way the block repeats.

What's new to you here, though, is the orange oval with "i" in it. By using this i, your inner blocks can know which time through the loop they are currently on. Here's how:

The block is a variable that acts like a counter. You use it any place you would use a number, and it will report the value that it currently holds.

Think of the variable like a box with a name—this one has the name i. This box is made for you by the block, and holds a different number each time through the loop. The first time it will hold 1, or whatever is the left number in the for block.

You use it by dragging from the source within the for block down to the slot in which you will use it.

For instance:

is the equivalent of