For many years we held classes for adult beginners monthly during the summer in a Civic Centre car park. Most learnt to ride from scratch in a single two hour session. For various reasons we had to discontinue these.
BikeAbility (Wales) used to offer classes at their base at the Dunvant RFC. These were discontinued during the Pandemic. Check with them for the current situation.
For general advice on getting started you should find this Bike-safety-guide helpful. It is not just about cycling safely.
If you can now ride a bike our Rides and Commutes page (near bottom) describes a variety of local rides including commutes from outlying districts to the centre of Swansea.