Just like in English with 'if', French use 'si' to talk about things that might happen, would happen, or would have happened, dependent on another event happening.
There are a few ways this can be formed.
Si + present event + present event
e.g. If you believe everything you see on the internet, you risk being a victim of fraud.
Si vous croyez tout que vouz voyez sur Internet, vous risquez de devenir victime de la fraude.
Si + present event + future event
e.g. If we arrive late, the teacher won't be pleased.
Si nous arrivons en ******, le prof ne…