boot – I have been trying to reinstall ubuntu on my laptop but now I am stuck in gnu grub and don’t know how to get out again

I first installed ubuntu on this laptop a couple of months ago, I dual booted with windows but just the other day ubuntu just disappeared. I turned on my laptop and it went straight into windows, as if ubuntu had never been there. I think it might be a windows update that’s to blame. I’ve made a new partition now and put ubuntu on a usb drive, but when I try and boot it, it doesn’t take me to the installation page, it just brings me to gnu grub.

Now it seems like this is a common problem and I’ve been looking at other posts about this for hours and haven’t been able to find a solution, or to even get a sense of what is actually wrong. I would really appreciate if anyone could help me, but bear in mind that I really don’t know much about these things so please explain like I’m a toddler, lol.