OIs there a way that I can ensure a unique entry in "Clients" and be able to use that info when referencing "Jobs.
make sure the clients table has an auto_increment primary key (call it id)
then add a client_id column to the jobs table, and link up each job to its client by placing the client's id value from the clients table into the client_id column of the jobs table for that particular job
for full marks, use the FOREIGN KEY syntax to declare the relationship explicitly
Could you explain the foreign keys concept a little bit.
a foreign key is a column on one table that has values which reference (i.e. come from) the primary key of another table
you can relate tables this way blindly, and control the values with application code, or better yet use the FOREIGN KEY syntax to register this relationship with the database, so that the database will ensure that no one and no application can ever insert a row with a foreign key value that doesn't exist in the referenced table