Trailhead provides a really nice overview of Salesforce Custom and Standard Objects and how they are structured https://developer.salesforce.com/trailhead/force_com_introduction/data_modeling/objects_intro.
The minimum steps required to set up an Object.
This video from Trailhead is a really good overview of creating fields https://www.youtube.com/watch?v=j95gONjVNFU#t=11
See Rules for Fields
Trailhead has a good overview of Relationships https://developer.salesforce.com/trailhead/force_com_introduction/data_modeling/object_relationships
Remember, Master Detail relationships are great, but you can always use triggers, or Rollup Helper to create calculated fields if you don't have a Master Detail relationship.