Looking for DUAL boot options From HDD to m.2 SSD. Alienware 17r2(2015) windows 10 w/creators update

I presently have a standard harddrive, gettng an m.2 ssd.. 500 gigs... My standard HDD is full to 800 gigs, and the drive is 921 gigs..  the M.2 ssd will only be 500 gigs..   How can I put windows 10 on my new m.2 ssd?  I cant clone, since the 1st harddrive is double the size of the new ssd... Can I somehow use a homemade "recovery" disk from dell for my system to do a FRESH install on the new SSD?  And Like I said, I dont want to completely MIGRATE my entire system to the new one, I just want to be able to be able to boot and run my computer from either one...   I need help and instructions please...