One of my most popular blog posts is originally from 2012 and focuses on SharePoint Calculated Column formulas: SharePoint Calculated Column Formulas & Functions – The Essential Guide – Tuomi Services Ltd.
While many of the questions people ask in the comments are asking about esoteric formulas or some weird quirks, a lot actually can be solved by an understanding of how to effectively structure nested statements in Excel. As explained on the original blog post, SharePoint Calculated Column formulas are almost on par with Excel formulas (with some exceptions).
I found a great resource at https://www.myonlinetraininghub.com/if-formula-builder
which provides a free (asks for but doesn’t actually require your email address) Excel sheet which is set up to help you prototype “IF” statements.
Instructions on how to use the Excel are on the linked page.