A bootloader is a little piece of software that starts up when you boot your computer, and it it turn starts up the main OS. Think of it a bit like rocket stages, or jump starting a car. GRUB is indeed the bootloader ubuntu uses. It can directly boot linux, and it also usually has an entry that you can scroll down and hit enter (under "ubuntu" and "advanced options for ubuntu") to tell GRUB to "boot" windows by handing off control to the windows bootloader. Your chainload command seems to just be doing the manual equivalent of doing that. (If any of this is wrong, someone correct me please)
I know I've accidentally deleted my windows bootloader before messing with partitions, but that doesn't seem like your problem here. If it was, trying to boot into windows would just give a "no media found" error.
It sounds like you can boot into windows, just inconveniently?
Do you want to boot into windows when you boot, automatically? This would mean you have to go into your motherboards boot menu and manually select Ubuntu each time you want to use it. If this is what you want, try going into your BIOS/UEFI (your motherboard's settings menu, usually delete or f11 or something as you are booting. Or the bottom option in GRUB, the "UEFI system settings" or whatever, is an easier way.), finding a tab that says boot and something that looks like "boot order" or "boot priority", and setting your windows install at the top, before your ubuntu install.
If, instead, you want to boot to GRUB, and then select either windows or Ubuntu within the menu, and windows just isn't in the menu, try this. Within ubuntu, run sudo os-prober
in the terminal (command line). If it detects your windows install, run sudo update-grub
to add the GRUB entry.
Hope one of these things helps, they should for the most common problems like this. I will say that you are pretty unlikely to actually damage your windows data, even if you make it unbootable, by messing up the bootloader. The bootloader is in a separate area and messing it up can leave the main os untouched. Still be careful, but don't worry too much.