How to use a WHERE in a query made with a DBConnector?

How to use a WHERE in a query made with a DBConnector?

Hi.
I am using a DBConector in my project but I need to perform a query where I need to use a WHERE. Until now I had always used the queries in the DBConector without any conditions and had not had any problems, but this time I need to put conditions on my query and I don't know how.
Could you help me?