Would an external CD ROM or USB drive hold any memory?

I have a small laptop, possibly an 'ideapad' and lenovo. It does not hold much memory. It has no CD Rom. I don't think I stored that much stuff and its already saying how its out of memory. So i'm thinking of getting an external driver, i believe it's a CD ROM and its hooked up using a USB cable.
I'm not so computer savvy, so would this CD ROM store memory or space?
I know about a flash drive. But can a DVD/CD ROM store any data/ files?

A DVD/CD ROM drive does not hold any memory on its own. It can only read or write information onto disks.

CD ROM reads only disks. What is on them from other drives is all that will ever be on them. No memory storage for you.
A writeable DVD or CD drive can store stuff that you put on CD or DVD disks to read back later. But what is written on it can't be changed or erased.
A re-writeable DVD or CD disk in that drive can be written on many times over and over, or erased.
But that method of storage is many times slower than an external hard disk or flash drive or thumb drive. You should get a USB external hard disk drive.

"out of memory" might mean hard drive -- in which case, and external USB plug in HDD will do the job.

it also might mean that the builtin internal RAM isn't large enough for everything you're trying to run at once. That MIGHT be upgradable… Check makers website under specific model number [it's in the number plate on the back].