It is fairly easy to create a USB boot drive for any LINUX
distribution. Make sure you have a USB stick that is larger than 2GB and you may find some sticks will refuse to boot correctly so if the first attempt fails try another brand of stick - go for a known brand like San Disk, Corsair
You have to set your PC's BIOS to boot first from USB Hard Drive and on some BIOS there maybe a second setting like "allow boot from USB" or similar and this also needs to be enabled. Getting in to the BIOS varies from PC to PC but it is usually pressing the F2 or Del key. Make sure you save the BIOS changes you have made usually by pressing the F10 key.
There are loads of LINUX distributions, but I would recommend Ubuntu as it is well documented and it is pretty easy to setup OpenCPN on it without having to compile it, which as a newbie is definitely not something you want to do.
Here is a good article on putting Ubuntu on to a memory stick...
Once you have your stick with Ubuntu on it, insert it in the PC and power the PC on (assuming you have made the BIOS changes). Follow the instructions and you should soon have a Live copy of Ubuntu running on your PC but not installed. This is good and allows you to check that all of your PC's hardware
is working under LINUX. Check your Wi-Fi adaptor, touch pad, sound card, Bluetooth, etc as these are typically the devices that LINUX has problems with due to no open source drivers.
Once you are happy that everything is OK install Ubuntu to your PC's hard drive - all of your Windows files, license
and data will be lost
Here are some useful links....
The OpenCPN install procedure looks complicated and I am pretty sure that last time I did this on newer versions of Ubuntu, that I used the Ubuntu Software
Center to do the install, but you may find that the Universal repository (website that hosts LINUX open source files) is not set by default so you may have to enable it.
The problem for people new to LINUX is that the amount of information online is immense and can easily confuse you. There are so many distributions, so much history
and so many different PCs and applications that you can drown in the sheer amount of information when you start searching online. Just take it slowly and use the latest 2013/2014 web pages and focus on Ubuntu guides that do things through the Ubuntu desktop
user interface (GUI) rather than typing commands in to the classic LINUX terminal.