Have a read of some of the pinned threads at the top of this beginners section.
Are you intending to commute? Does where you live have a lot of segregated cycle paths or will you be mainly on road, or a mix?
I would first familiarise yourself with the traffic laws where you live.
Second, there may be organisations or charities that run lessons on introducing people to cycling on the roads. A few years back as I hadn't been on a bike in 35 years and wanted to start commuting I took some free lessons from
City Connect, which really helped. Apart from that it's a case of getting out there.
Go for some short rides near you to get used to it, and explore, find some routes. Try planning some routes online, and then use google street view to scope them out before you ride, to identify places in advance where you might not be confident (big traffic junctions, major roads). Cycle.travel is a great free website for this and tends to be much better than Google at planning bicycle friendly rides.