I have Locked myself out of my phone because I entered too many pattern attempts. I can't sign into my Google account because my wi-fi isn't turned on. So I need to factory reset it. I'm just wondering what will I lose. My photos and videos are saved onto my phone, will I lose them? If there are any other options in getting back into my without factory resetting it, it would be greatly appreciated. Thanks By the way I have a Samsung Galaxy Xcover
A factory reset wipes the internal storage of your phone. This includes all apps, their settings, and all the files and data saved onto your internal storage. Any apps or other content you've downloaded from Google Play, you can download again (you don't have to pay again).
If you previously updated the system or flashed a custom ROM, it will still be updated or have the custom ROM (because system updates update the ROM, not the internal storage.) Similarly, if you rooted the device or unlocked the bootloader, it'll still be rooted or unlocked.
It won't erase any data from the SD card. Usually photos and videos are saved onto the SD card but it depends on the software and the device.