Hello @OrielaB and welcome to TWB!
As @soke35 kindly mentioned, you don’t need to be approved to do a translation work. I believe that by the time you wanted to claim the task, another volunteer had already claimed it. Another possible reason is that the task you wanted to claim is only available for verified translators.
There are always several choices of tasks to claim for sure! If you’d like to learn more about how to claim a task, take a look at this tutorial.
Also, you may find it useful to take a look at the translator’s toolkit that includes information and instructions on how to use the TWB Platform.
Please let us know if you have any questions