Is one supposed to use the holy water before entering the chapel or after? I only saw people making a sign of the cross with it on themselves as they left the service.
Either or both. I do both. You should know, Candice, that I used to think of 'holy water' as one of the silly superstitions of Catholics. But I see it now as a sacramental act of receiving a blessing from Christ while entering a sacred space where Christ Himself is present, and taking His blessing with me when I depart. There's no magic in the water. But it has been prayed over ("blessed") and consecrated (set aside) to a sacred use. The sense of it is almost that, as you apply the water to yourself, you are applying the blessing too. The Biblical precedent for this is in the use of sacramental anointing oils and cleansing waters in the Old Testament. Catholics make great use of 'sacramentals' like this - physical objects with a holy meaning and, being more than symbolic, carry a real blessing with it. The crossing of oneself with the water is, in a way, a remembrance of the baptismal waters, too, whereby we were first cleansed and united to Christ and His Church.