As you can see, you can make it as complicated as you want. The for -loop is useful when you have to have the same task repeated a number of times. The for -loop works be first initialising a variable, then do a test, and if it is true, then execute some code. After the code have been executed do some other code, that will increment the variable and then execute the main-code again. And you're perfectly right.
First lets have a look at the for -loop.
It simply increments the variable by 1. It is used when you don't know in advance how many iterations you'll need. View the source of this page.