Search in custom table

Hello,

I am developing a module that will query a table called companies(id, status, name, contact_fname, contact_lanem, contact_email, address). I need develop a search that will into a node and that will consult the name, contat_fname fields and contact_lname fields.

I would like to know where to start, where I can find examples to study and do what I need.

Any help will be very welcome