Need help understanding Disk Management

1st is your EFI system partition, do NOT remove, you need it to boot.

2nd is an OEM (Dell) Diagnostics partition - can be removed if you are happy to rely only on BIOS diagnostics.

3rd (and never shown in Disk Management) is a 16 MB MSR (could be 128 MB but I'm going to guess your system is old enough that it is only 16). Microsoft wants you to leave it alone. Some members here at TF will disregard that and remove it. I toe the MS party line and leave it. You can find the size using Diskpart - let us know if you need any tips on using it.

Partitions 4 and 6 are Recovery Partitions that very likely include the Windows Recovery Environment (WinRE). Only one of them will be active - you can execute "reagentc /info" at an elevated (admin) command prompt to find out which one is active. Up to you whether to keep one or both, depending on whether you need the Windows recover tools or simply rely on a backup/imaging program to recover from problems.

7th is your Dell recovery image for resetting to out of the box state. I opted not to keep mine as I have a well stored Macrium Reflect image of how mine came out of the box and I wanted to reclaim the disk space. IOW, I feel this partition is optional but you should make up your own mind now that you know what it is for.

Ironically, none of them shown are empty, only the one NOT shown is likely empty.