When my husband was a preteen he collected old bicycles and put together one or two good ones which he sold.
Both he and I did yard work. He cleaned the whole yard. I just raked leaves (got paid $1 per job).
What's in your neighborhood? Are there big trees with lots of leaves? Are there plants with overgrown weeds? Are you willing to rake up dog poo?
When you go to offer your services, you should state what you are willing to do and the price. Such as: Hi my name is Ryan; I'm trying to earn some money. I notice your plants have loose grass (weeds) growing around them. Will you pay me $5 to weed that area? If they say no and close the door - walk away. If they look like they are thinking - wait. You can ask them, "What do you think that job is worth?"
It's their word of honor that they'll pay you after you do the job, and most will, but not everyone is honorable. My husband had done a 2 hour yard cleaning job and the neighbor said thanks, but I don't have any money.
11? LOL! When I was 11 I was focused on spending money not making it. Play some video games! Go play baseball, go swimming! Just have fun!