All my assets are free, but can you use it in your commercial project? Short answer: Yes!
1. Can you use my assets?
All assets, if not explicitly say otherwise, are under standard Asset Store Terms of Service and EULA as Non-Restricted Assets. As we see in ELUA:
2.2.1 Non-Restricted Assets. The following concerns only Assets that are not Restricted Assets: Licensor grants to the END-USER a non-exclusive, worldwide, and perpetual license to the Asset to integrate it only as incorporated and embedded components of electronic applications and digital media and distribute such electronic application and digital media; reproduction and display in distributed physical advertising materials is permitted solely for marketing purposes in respect of such electronic applications or digital media.
So, you can use assets wherever you want as long as it's end product such a game, movie, etc. We can see further:
Unless you have been specifically permitted to do so in a separate agreement with Unity and except as permitted under the Unity-EULA, you agree that you will not reproduce, duplicate, copy, sell, trade or resell any Asset that you have licensed from the Unity Asset Store for any purpose.
You CAN'T sell assets as just assets with your name as an author.
2. Check Unity Support Pages
Unity has lots of handful of articles on their support page. Here is an excellent example for one of: Can I Use Assets From The Asset Store In My Commercial Game?
3. Do you have to credit my assets?
No, you don't have to. If you want to, it will be appreciated, but it's not a requirement of use.