A repayment mortgage spreads the cost of your loan across a set time frame (usually 25 years) including interest. By the time you reach the end of your mortgage term, you will own your home outright, after repaying both the amount you borrowed initially, plus the interest.
Typically, the first few years are weighted towards the interest, while the remaining time is used for paying off the actual value of your mortgage. This is done due to the interest being calculated from the present outstanding balance of the mortgage, which decreases as more of the principal is repaid.
As long as you meet each monthly payment, your mortgages will be paid for in full at the end of the term and as long as you have no other borrowing secured on it, you will own your home.