Most languages have a separate verb for this. English builds it out of there plus is or are. Spanish has hay, which comes from haber.
hay = there is, and there are
For once English changes and Spanish does not: hay covers both singular and plural.
Resist the temptation to say "habían" for there were. It is always había.
Hay alguien aquí que quiere hablar con usted · Hay dos personas aquí que hablan español
Combine hay with que and you are specifying something whose existence you are unsure of. That subjectivity takes the mood tense.
Somebody replying with what actually exists is simply stating a fact, so no mood tense there.
In there has to be something, that be is not ser or estar. It comes from the invisible verb behind there is, so it is haber.
tiene que haber = there has to be
Tiene que haber algo que puedas hacer.
A good demonstration. English says there were two people that spoke Spanish with a point past, but Spanish wants the line, because being a Spanish speaker was not something true only for that moment.
Había dos personas aquí que hablaban español
Use the point, que hablaron español, and you are no longer saying they are Spanish speakers, only that they spoke Spanish at that time.
Two constraints operate at once: it can only appear in certain structural positions, and only to convey certain meanings or feelings.
The fact that Spanish requires you to express these feelings, and pay attention to them, says something about the language itself.
Use of the mood tense shifts slightly between dialects, and even between individuals, which is their own idiolect. So this is not something to obsess over getting right. Listen actively, analyse, and enjoy working it out.