Can I use the resources in the projects, in the learn tab on the left for my commercial game?
If so, do I have to credit the creators of the projects?
Yes, in general you can - if you are using the Unreal Engine - but you should check each license. If you click on the “book icon” on each project, the license will be stated. E.g. “Strategy Game” says "Licensed for Use Only with Unreal Engine-based products. You do not need to do any crediting.
From Wiki:
Q: Can you use the content in the marketplace for commercial use ?
A: You can use all of the free Epic content in the marketplace commercially in any games you build with UE4. This includes all of the content residing in example projects. For example, all of the weapons, meshes, sounds and materials in Shooter Game. Tappy Chicken even!