As Mrs. Sally noted, the parish may well participate in an on-line service. Mine uses ParishPay. The parish actually strongly encourages people to go that route if possible, as it provides them a more predictable income stream month-by-month.
If you are as unreliable as I am about remembering to bring the checkbook, even just once a month, another option would be to set up your parish as a monthly “bill” to be paid through your bank. DH & I actually have this running in addition to ParishPay, since we wanted to provide regular support to the parish outreach program that assists people with groceries, utilities, etc. There wasn’t any way to designate part of our on-line monthly donation to go to Outreach, so I just set up something separate at the bank. Outreach receives a small check from us every month in the mail and I don’t have to keep remembering to take care of it…
Good luck as you prepare to become Catholic!
PS One random point: since DH & I have young children, we still dole out a few dollar bills to them to put in the basket most weekends, since we’re also trying to train them in the habit of giving. They don’t see (or understand) about giving money online, so we figure it’s good for them to get it ingrained at an early age that supporting the Church is a serious obligation, even if the amount is small.