I hope you are keeping well. I am working at international organization as a Deputy Data Manager. I have created the entire database through ODK build and as well as excel and now I don't know how to proceed. I mean how to upload the the excel form on Aggregate, I don't know how to install Aggregate? how to configure it? and finally how to upload the excel form on Aggregate? Could you please advice on the above matters.
You can follow the documentation for instructions on Aggregate installation: https://docs.opendatakit.org/aggregate-setup/
However, I would suggest you explore Central. This forum post discusses the features currently available. We expect Central to become a viable replacement for Aggregate for most users by June 2020, if not sooner! I think the instructions for setting up ODK Central on Digital Ocean are much easier to accomplish than setting up Aggregate: https://docs.opendatakit.org/central-setup/
Also - it depends on what you are trying to do.
If this form is for many people to use then Central or Aggregate will be best.
If you have a single user in mind, you could just upload results to a Google Sheet which is easier, but has limitations.
( https://docs.opendatakit.org/collect-connect-google/ )
If you have created an Excel XLSForm then you will need to convert this to XML to upload to Aggregate (if you choose to use this as your back end); you can do this online at: