Backup programs offer many choices of places to store backups. By far, the easiest and least expensive of these is an external hard drive. (The term 'portable' hard drive simply means an external hard drive that is small enough to carry around in your pocket.)
For storing backups you do not need a fancy-shmancy external hard drive with additional software and ultra-fast speed. I use a years' old Toshiba Canvio Basics drive and it works very well. A plain black 500GB version costs less than $50 and will last a long time. (At the moment it's $44 on Amazon.)
Full disclosure: There is a learning curve to image backup programs, but nothing you can't climb. These programs can do lots of sophisticated things with backups, but all you need to concern yourself with are the basics of making a Full backup. One of the great things about Macrium Reflect is that it was developed in Great Britain, so the user instructions (known as the knowledgebase) are written in the Queen's English.
More disclosure: Like many other backup programs, Macrium Reflect has a free version and a paid version. You might want to start with the free version, which has limitations, but is a great way to learn how to use the software. I myself have the paid version because I appreciate the extra features it offers plus it gives me access to technical support from the developers.
Take it slowly and you'll do great. But I think you'll find that backing up is a lot like Oreo cookies: Once you get started, you want to keep on going.