I am a business analyst. I use Tableau a lot but have limited knowledge about the back-end of Salesforce. The majority of our company's data is stored in Salesforce and our data team does not support business users for understanding such topics.
In many of my projects, I use the Salesforce connector inside Tableau to extract Salesforce tables, but it requires knowledge about joins relationships among tables. Most of the time, I can guess correctly about the primary key among tables, but I still want to learn systematically about the data structure and have my data independence.
So, how do I learn the data structure by myself? Or how do I ask specific structure questions to data team so I don't trouble them as much?
Do you have Salesforce account with "Customize Application" permission? If you don't have in production - maybe they'll be willing to promote you to sysadmin in one of sandboxes.
If you do - Setup -> Schema Builder might be easiest tool to visualise relations. It's bit old, flash-based but pretty neat way to model relationships. https://trailhead.salesforce.com/en/content/learn/modules/data_modeling/schema_builder
Another one might be workbench, http://workbench.developerforce.com/ It's not as neat but lets you experiment with metadata & queries, learn which object has what child relationships...
For standard objects if you have a primary key / foreign key you can use some lookup tables to learn more about target table. All Account Ids in all SF instances start with 001. Contacts with 003, Users with 005... Combine some blogs like http://www.fishofprey.com/2011/09/obscure-salesforce-object-key-prefixes.html with https://developer.salesforce.com/docs/atlas.en-us.api.meta/api/sforce_api_objects_account.htm and it's a good start. Won't help much with custom objects and fields (specific to your company) but well.
It's bit "meta" but you can query info about tables and columns too. After all - you might be more comfortable in Tableau ;) Querying Salesforce Object Column Names w/SOQL might give you some hints.