Repayment is usually taken automatically using direct debit on your pay day. When you sign a loan agreement online you also set the agreed repayment date/s with your lender.
Every lender has their own repayment policy when issuing loans up to 6 months. Some will need most repayments to happen sooner than later. Others spread it more evenly or defer the bulk payments. The total cost of the loan will vary accordingly. Most will allow early repayment but there could be a minimum period you must borrow the money for. Thus, is it so important to compare the lenders repayment schedules to see how much you must pay in the end.