To answer the 1st part of your question, we join the tables depending upon the relationship that we have established ( as per the normalization process). The intention of the join should be able to identity unique using the key values( which can be composite key also).Keep in mind for join use all the keys that have been defined as PK, eliminating a single key could bring in redundant data. For the syntax side alwys use ANSI SQL-99 format :-
JOIN <newtable> ON ..
The earlier syantx (ANSI-SQL 92) used to be
FROM <mytable>, <newtable>
WHERE <filter clause="">
The problem with the '92 synatx in SQL Server is that this would create an cross-join which would all together impact the performace of the query.
Now, for views :- As per the definition of view, these are logical structures that have their physical structure stored but not the data,meaning, a view when created contains only the structure the data is fetched from the actual tables when we query a view (unless we have a materialized view in place).
You, can always refer to the BOL for further readings.