A latch forces serialized access to certain memory processes.

A lock is a mechanism to ensure that more than one user cannot change data in a table (row level locks) or table structure (table locks). Locks can be shared or exclusive.

There are lots of V$ synonyms (widely referred to as views) that are helpful in tuning and gaining an idea of what is happening on the database.

Look at v$fixed_table to see a list.

Good luck.