Hey there and welcome to the Samsung UK and EU Community Forum
It would appear your device supports Micro SD Card memory. As mentioned above, you'll need to purchase a Micro SD Card in the correct format (Google search this or look on Samsung website). Pop it in your device, format it (follow on screen instructions) then you are good to go.
Couple of things to note....
1. If your Micro SD Card fails, you'll likely lose the data
2. You may be better off taking out a subscription such as Google One, Microsoft One Drive which, although you'll pay each year, you are less likely to lose your data (images and videos etc).
Remember to ensure your device is backed up too just in case.
S24 Ultra