The idea is that today we have certain governmental programs that are meant to help people/families when they are unemployed, when they can't pay for their medical costs, for education,... These programs are payed for with taxmoney. This comes from all kind of taxes like VAT, income tax, ....
But research shows that with today's budget a basic income would not be feasible. If you replace the current programs by a basic income then you might need to double that budget. If you raise taxes maybe we can pay for it.
Higher taxes could be found in higher VAT on everything we buy, higher income tax, taxes on pollution or carbon emissions, ...
It's clear that at the end the basic income would be a redistribution of wealth. So wealthier people should contribute more, and less wealthy people less. Otherwise it wouldn't make much of a difference to change the whole system.