in Mr's example there would be three fields, one from table 1 and two from table 2.
You can pick whatever fields you like for the result set.
Mr has used aliases of the table names calling table1 t1 and table2 t2, you don't always have to do that but it's very helpful, and the only way to do a join on a table with itself.
If you are joining 2 or more tables and they have fields with the same name you have to resolve the ambiguity by naming the fields in the
table.field
format.