Blending vs. Joining in Tableau

Joining Blending
When to use Single source (one excel file) Multiple data sources (two sources/ excel files)
Example two sheet tabs within a single Excel file information was stored in separate Excel files you would need to do a data blend in Tableau.
Must have one common field between each other

Blending: When you are working with more than one data source, you blend the data

Joining: When you are working with one data source, then you are joining the data onto a common field.

If the two column headers are an exact match, Tableau may automatically establish the link for you.

Otherwise if you have columns with different field names then you might have to form relationship using edit relationship option on Tableau