Most of the boxes that are rated as Easy are accessible to newcomers, they might take you a little bit to solve at first but once you get your methodology down and have experimented with a few tools you should be able to breeze through them. Here are a few nice easy boxes that take little time to solve:
- Bastion (still accessible from the free labs right now)
And the currently active ones:
There are many more available between the retired challenges, I listed the ones I remember liking. If your friend needs help he can always join the public discord server and ask in the dedicated channel.