Condition
What must be true for this to happen or apply?
Meaning
A condition makes one situation depend on another. It can describe a real possibility, a regular link, or a situation that is only imagined. Languages can use linking words or verb forms, and some leave the link to context without a separate condition marker. Unlike Imagined situations, Condition is about the link between two situations, not whether either one is real.
How to spot it
Find the situation that must hold for another event to happen or another statement to apply.
In your native language
English commonly introduces conditions with if; unless means if ... not. For an ordinary future possibility, the if-part usually uses a present tense even when the other part uses will. For a less likely or imagined situation, English often uses a past form after if and would followed by the verb's base form, its form without endings, in the other part.
If it rains tomorrow, we'll eat inside.
Rains is a present form, but tomorrow makes the future time clear.
You can't use the pool unless you're a guest.
Unless you're a guest means if you're not a guest.
If I had a bigger kitchen, I would buy a larger table.
Had describes an imagined situation now, not a past event.
In your learning language
Spanish links a condition to its outcome with si. For an open future possibility, si normally takes a present verb form, not a future form. Imagined or unlikely present or future situations often use the imperfect subjunctive (imperfecto de subjuntivo) after si and the conditional (condicional) for the outcome, as in hiciera and comeríamos.
Si hace sol, comeremos en el patio.
If it's sunny, we'll eat in the courtyard.
Hace is present, although the condition concerns the future.
Si hiciera sol, comeríamos en el patio.
If it were sunny, we would eat in the courtyard.
Hiciera and comeríamos present the situation as imagined rather than as an open prediction.
Learners whose language allows future forms after a condition word may produce *si hará sol. Learners whose language uses the same imagined-situation form in both parts may put a conditional form after si, where Spanish needs a subjunctive form.