A conditional sentence is one with a clause introduced by if.
If you are doing these things, you are very stupid.
In Latin this sentence would be:
si haec facis, stultissimus es.
A condition referring to a future event uses a future tense verb in Latin, but English prefers to use a present tense verb instead.
si Romam ibis, multa et pulchra videbis.
If you go to Rome, you will see many beautiful things.
A negative condition uses nisi, translated as if not or unless.
nisi paucis horis magister redibit, pueri discedent.
If the teacher does not return in a few hours, the boys will leave.
The condition (AKA the protasis) can be in the past, present or future tense, and the outcome (AKA the apodosis) does not have to be in the same tense.
cras moriemini si heri hoc scelus fecistis.
You will die tomorrow if you committed this crime yesterday.
- si quaeris, invenies.
- si sic locutus est, non amicus meus est.
- nisi auxilium paucis diebus adveniet, omnes moriemur.
- mater non laeta erit si hoc non factum est.
- nisi hostes urbem ceperunt, cives felicissimi erint.