The message means exactly what it says: There will be no more updates for Windows 7 from Microsoft, including anti-virus and anti-malware patches. So (in theory, at least) your computer will become more vulnerable to attacks from malicious software from now on.
Microsoft did offer a free upgrade to Windows 10 for quite a long while but you obviously decided against accepting it. (That's not a criticism! I decided against it too, for a variety of reasons).
In theory you can now choose either to
(a) buy a new machine with Windows 10 pre-installed ; or
(b) pay for an upgrade to Windows 10. However that will cost you £119.99 for Windows 10 Home or £219.99 for Windows 10 Pro.
Alternatively though, you can either
(a) continue to use Windows 7 anyway (see below) ; or
(b) use a backdoor route to upgrade to Windows 10 for free (see further below).
I'm curently continuing to use Windows 7 (although I might buy a refurbished Windows 10 machine in the not too distant future). The chances of anything nasty happening are actually very low anyway (certainly in the short term) and people who keep seeing the message that you're getting can easily disable it by following the instructions here:
https://www.sevenforums.com/tutorials/418989-disable-windows-7-end-support-reminder-notifications.html
The backdoor route for upgrading to Windows 10 requires you to know the product key for your existing version of Windows 7. There are plenty of programs that can find it for you but my own choice would be Belarc Advisor:
https://www.belarc.com/products_belarc_advisor
After noting down that product key, go to the Microsoft website to find the download to upgrade from your existing version of Windows 7 to the SAME version of Windows 10. (i.e. if you're using Windows 7 Home, you need to find the download for Windows 10 Home. If you're using Windows 7 Pro, you want the download for Windows 10 Pro).
Follow the instructions from there for upgrading to Windows 10. When you're asked for your Windows 10 product key, simply enter the old one you had for Windows 7; it will work fine!
You should note though that the hardware on your laptop might not be fully up to running Windows 10. If it can't handle it at all, you'll see a message advising you of that and you'll still be left with Windows 7. If it can only barely handle it, you might find that your laptop runs rather slowly under Windows 10.
It's not clear to me as to why you can't continue to use iTunes with Windows 7. (Have you tried changing your password, as per my answer on your other thread). However it's equally unclear to me as to why you should want to have iTunes on your computer at all. Magazines such as Computer Active and Web User periodically contain articles listing the software that should NEVER be on any PC and iTunes is included every single time! There are far better alternatives!
If you need an alternative to iTunes, try MusicBee
https://getmusicbee.com/
or MediaMonkey
https://www.mediamonkey.com/
If you decide to give up and buy a Windows 10 laptop, take a look at these refurbished models (from a company that I've got total faith in - their products and customer service are both excellent):
https://accomputerwarehouse.com/product-category/cheap-refurbished-laptops-uk/