A task or job is simply a set of instructions that you follow, and get paid for it. For example, there may be a task to categorize images or videos, make google searches, etc...
Most tasks can be completed multiple/unlimited times while others may be limited to a certain number of completes, a message will display on the screen to explain this.
Certain tasks will require you to train for the task before you can actually complete them. Meaning you will be evaluated to see how well you perform in doing the task before you are able to complete it.
Pay attention to any instructions in the tasks or hints attached to questions you answer incorrectly -- these are critical to your success in completing the tasks.
Your accuracy and credits are displayed in the top pane of the task. Please familiarize yourself with the tasks page before you attempt any.
Many of you will frequently fall below the minimum accuracy threshold for a particular task, at which point you are no longer permitted to continue working on that particular task. Do not get discouraged as this is to be expected and does not reflect a bug. You are then most welcome to participate in any of the other available tasks.