How do people learn to land an aircraft properly when they have to pay for every landing?
It varies, At bigger fields, resident aircraft (from a flying school) will or may get a reduced landing fee. At some fields, e.g. Old Buckenham, membership means that you don't pay at all. At small grass strips there may be no charge. But yes, you are right that it can be a significant expenditure when learning to fly, as it was for me at Norwich. The situation is a bit better now that training in the UK does not have to be at licensed fields.