Help Understanding Enumerable.Join Method

Question

Yesterday I posted this question regarding using lambdas inside of a Join() method to check if 2 conditions exist across 2 entities. I received an answer on the question, which

Answer 1

This query is saying join TableA to TableB where TableA.someFieldID == TableB.someFieldID and selecting the results from TableA and seeing if there are any results at all

In terms of SQL think of it like this, even if it's not Linq-to-SQL...if you are familiar with SQL maybe this makes more sense:

Select Count(*)
From TableA a
     Join TableB b
       On a.someFieldID = b.someFieldID

Then checking if Count(*) is > 0