A one-time contribution is a larger sum that you invest in one go. This could, for example, be an amount you saved up in addition to your emergency fund. Perhaps, it’s a bonus or an inheritance.
Your monthly contribution is an amount that gets invested in your investment plan each month. Once you set it up, you don't have to do anything else. It's a great way to work towards your financial future as you go.
The most important thing is to get started. We recommend that you start investing continuously as soon as you feel ready to make a habit out of it. Standing by the sidelines and "waiting for a good market moment" to invest a larger one-time payment is not advisable. It is better to get started with a small, monthly contribution and find out under which circumstances investing feels best for you.