If you want to make an album cover and have it printed professionally, then I have to warn you, Linux will not get you very far. I keep an eye on it, because I like Linux in general, but it’s really nowhere near usable with print-related graphics stuff.
It lacks on all fronts. Software packages are ok for casual use, but lack some more robust features. GIMP still doesn’t do CMYK for eg.
I could write a whole list of things that just don’t work in Linux, but I’ll spare you the rant.
This said, an ideal Linux based workflow for print graphics would look like this, depending on what you’re after one ore more applications will of coruse be omitted:
- prepare all the photo/bitmap material in Gimp
- prepare all the vector graphics in Inkscape
- prepare any 3D rendered graphics in Blender (which is actually where Linux does have a really great software package!)
- then asseble / layout everything in Scribus and produce a final CMYK PDF/X (PDF/X-3 probably) file from there.
Scribus has a horrible UI and does make even simple things super akward to get done, but it might work for you, maybe I’m too biased by 20+ years of working with Indesign.
Also don’t underestimate the impact of colour management on your work.
In general I would advise against sending printers anything but a PDF/X file.
In general my advice is: make some desginer friends and trade some cover design with them! 
edit: I was referring too much to a Linux environment in my post, but indeed the title only talks about open soruce software not necessarily the OS.
My points don’t change though. If you’re not on Linux I’d suggest to take a look at the Affinity programs. Not FOSS, but they are relatively cheap and get the job done really well!
