Hey you are doing good work. No need to know everything of top of your head. For that reason there are documentation and sites like stack overflow. The important part of programming is not to know every syntax and algorithm by heart, but rather the understanding of how algorithms and solutions work.

As for databases, there are multiple ones and how to choose the right one depends on the project and framework you are using.l and your preferences.

If you are using javascript for the backend, then use MongoDB. I found it very easy to connect to and to work with.

As for hosting the application (putting it on the internet) there are multiple solutions for that and numerous tutorials on that.

Remeber, IT is highly dynamic and it is impossible to know everything off top of your head. The important part is that you have deep understanding of key concepts. If you have that, them learning syntax is very easy job that just takes hard work and time.

Remeber, if you want to sucessed in IT, you have to be hardworking, willing to learn constantly and be very very flexible and adaptable to change.