turn off your computer, plug in the key, press the power button to turn it on, then immediately and repeatedly press your boot menu key, it's probably of the f keys above the numbers on your keyboard, if you have an hp laptop it's going to be f9 otherwise it's often f12 but that can be any other one, try googling it, then you will have a menu appear which lets your select "usb something whatev" select it and press enter, if that doesn work, you'll have to learn all about configuring your bios to run linux
alright that's good, that means it's seeing the key as bootable, you need to enter the bios config, same procedure, but it's another f key, then you will find an option that's called secure boot and you can change it from "enabled" to "disabled", on some bios, you first need to erased the stored secure boot key first
if that doesn't work, look up how to enter your specific laptop's BIOS settings. There, you should find the boot order menu to switch to booting from that usb.
Also maybe try to search for a video on how to create and boot using a live session. People here are giving wonderful advice on how to do it but seeing it done visually will be the easiest way to understand it
this might help with secureboot. By the way, Googling your problem concisely (e.g. ventoy secureboot acer laptop) can help find solutions, or at least give you ideas to try before asking here.