It's too basic. I thought it was a practical example, so I bought it even though it was relatively expensive, but it's below my expectations because it's a common foundation that you can find if you search the Internet a little. It's not just a foundation, and it only explains the functions without any basic concepts. There's no explanation for the parameter values of existing functions, except for those that require you to enter them. You just enter the parameter values yourself and move on without any explanation. Also, things like fragmentMap don't work at all as in the lecture, and they aren't updated. For the above reasons, if you don't use Firebase, this is the lowest-level Kotlin lecture that's expensive.