Create Report From Scratch?
Via the UI, you'll need to create reports using one of the templates available (e.g., from /civicrm/report/template/list?reset=1 ).  If you have coding experience, you can create custom reports from scratch, yes.  Here is the report reference from the Civi wiki: https://wiki.civicrm.org/confluence/display/CRMDOC/CiviReport+Reference