Okay, so imagine you have a big toy box with all your toys inside. Now, imagine you want to pick some toys to play with but you don't want to take out all the toys at once, so you make a list of the toys you want to play with. This list is called a bill of resources.
In the same way, a bill of resources is like a list of things that a project needs to make it happen. It's like a plan that tells everyone what things they need to get and how much it will cost to make the project happen.
For example, if you wanted to build a treehouse, your bill of resources might list things like wood, nails, a ladder, and paint. These are all things that you need to buy or collect to make your treehouse.
So, a bill of resources is basically just a list of all the things you need to gather before you can start a project. It helps you plan ahead and makes sure you have everything you need so you don't run out of supplies halfway through.