It is a common expression used to express confidence or certainty about something.
Here are some examples:
* Estoy seguro de que vendrá. (I am sure that he/she will come.)
* Estoy seguro de que lo logrará. (I am certain that he/she will achieve it.)
* Estoy seguro de que te gusta este libro. (I am sure that you like this book.)
You can also use it to express your personal belief or opinion:
* Estoy seguro de que el tiempo va a mejorar. (I am sure that the weather will improve.)
* Estoy seguro de que este es el mejor camino. (I am sure that this is the best way.)
Remember that the word "seguro" can also mean "safe" or "insurance," so pay attention to the context to understand the meaning correctly.