I need help downloading and configuring the central ODK
There is documentation on setting up and configuring ODK Central: https://docs.getodk.org/central-intro/
Please read through that and come back with any specific questions you may have - we'd be happy to try and help.
Another option is to pay for hosting services via ODK Cloud by Get ODK. You will support the project and get a fast, reliable, and secure platform for your work. It is the same software but without the hassle of self-hosting.