In terms of getting used to cycling then you could do worse than starting near Victoria Quays and riding up the Five Weirs Walk all the way to Meadowhall and along Blackbrook and even as far as Chapeltown. Its almost all off road with a few crossings and a range of twists and turns. There will be people but no cars except the crossings.

Pretty much ideal except there isn't a lot to look at along the way. Much better than doing lots of loops of a track.

If that goes well then from the same starting point you can take the tracks over the roundabout and along the Trans Pennine Trail. Again, mostly off road with the exception of a few minor roads and crossings. The benefit here is that the riding is a little more technical and there are some hills to help get used to riding those and using gearing a bit more proactively. You can take that out as far as Rother Valley Country Park or just turn around when you think you've gone far enough.

Doing some out and back rides on both of those routes should be a confidence boost for any learning rider.