Okay good. I thought the phone was stuck on the Odin download screen. You can also factory reset the device, as well as wipe the cache partition, from recovery mode.
The white spot on the screen is an oddity. It doesn't look like an icon to me, given it's positioning half in and half out of the status bar. Assuming it's not an icon that can be tapped, I'd table this one for the time being.
Since the device is up and running, the first thing I'd do is make sure everything's backed up, if you haven't done so already. Also try to think if there are any apps you've installed recently. Maybe there's something new that isn't playing nice.
If the phone is acting buggy, try running it in safe mode for a day or two and see how it does. In safe mode, only system apps are available – all third party apps are disabled. So essentially, only apps that the phone came with will work. Bonus: you'll likely notice it has a bit more zip to it, since none of the processes and services of third party apps will be running. How to access safe mode
If it seems to do better in safe mode, consider deleting any apps and files that you don't use anymore. Actually, consider doing this regardless. If you're near your storage capacity, this can supposedly cause performance problems. Note that system apps can't be deleted, but some may be carrier (Verizon, at&t...) and manufacturer junk – often referred to as "bloat", that can be disabled. You can also delete the storage of those apps.
That's probably enough for now. Hopefully you get on alright with it!