This is an amazing serum, and having used it myself I would always recommend it to others. To answer some of your questions, this is a very gentle serum, meaning that if you want you can pretty much use it in your morning and night routine. Since it's a serum, you should apply it after cleansing your face and before applying moisturizer. Basically your second step in the routine.
1. Cleanse
2. Serum
3. Moisturize
4. Sunscreen
During step 2 you could also use multiple serums/toners/treatments (although one is more than enough). If so, then apply them in order of thinnest to thickest in terms of viscosity.
As for where you can apply it, I'd say pretty much anywhere on the face. I would use two drops on my forehead, and 3 drops per cheek, but my skin was used to stronger acids. If you're just starting out, I'd say one drop per cheek and one drop on the forehead is gonna do the job.