Welcome and glad you joined.
It's kind of difficult to start out DIY'g when you are still trying out new equipment and establishing your taste favorites. One shot flavors are for those interested in mixing their own and want to start out simple. One shot flavors (OS/Flavor Blends) are premixed flavors that are only designed to be used on their own and mixed with a base of Propylene Glycol, Vegetable Glycerin and Nicotine (at least one/two/all of the three).Say you use three flavors at 4%, 3% and 2.5%. The one-shot/concentrate is just an entire bottle of those three flavors in the correct ratio. One shot mixing is supposed to be close to the flavor promoted on the bottle. These mixes may allow some adjustment of the strength (percentage) of the mix. OS Mixing can be a good introductory to DIY. One shots and flavor blends are simply added per directions to the mixer's desired mixing base, Shake and Vape (SnV) or steep as directed.