1. Subjunctive with the unknown
Verbs like buscar, querer, or necesitar plus que are used with the subjunctive when they introduce something that is not known for certain.
Use the indicative for the first verb and the subjunctive for the second verb.
Quiero una computadora portátil que no cueste mucho.
I want a laptop computer that does not cost much.

2. You also need to use the subjunctive with expressions that ask about something that may not exist.
¿Hay... que... ? ¿Conoces... que... ? ¿Tienes... que... ?
¿Tienes un teléfono que toque música?
Do you have a phone that plays music?
The subjunctive is used in a similar way when these expressions are used with no to say that something may not exist or definitely does not exist.
No conozco a nadie que publique poesía.
I don’t know anyone who publishes poetry.

3. To talk about things that definitely do exist, use the indicative.
Hay un sitio web que tiene la información.
There is a Web site that has the information.