This is the 359th most frequent Czech word.
byl
"Byl" means "was" in English.
In this sentence, 'byl' is used in a conditional context, part of a hypothetical situation.
Kdyby byl lepší den, šel bych na výlet.
If the day were better, I would go on a trip.
'Byl' here functions as part of a polite subjunctive structure asking for assistance.
Byl bys tak laskav a pomohl mi?
Would you be so kind as to help me?
Here, 'byl' is used as the past tense of the verb 'být' (to be), indicating a past action performed by the subject.