This is a great topic to discuss because a lot of people do not understand the difference or don't do the process correctly for the way they decide to treat their water. Either choice is designed to help with cloudy water (dead algae, etc) and to clear it up. So let's get started so we can help you choose which is the best method to treat your water.
Clarifier is a great choice if you have time to wait or don't desire to drain out part of your pool. It is also reasonably effortless on your part. There is not much physical work with using this.
How it works is it takes all those small particles and joins them together (through a technical term coagulation) making bigger particles so the filter will catch them and pull them out of your water. The result will be a clear pool. If you don't need the results right away then I would go this route.
What I would recommend is to make sure you start with a clean filter because it will be causing a small pressure increase in your filter but all the stuff it's bringing into it. You also want to make sure all of the valves are open so you get full circulation. Then you want to evenly apply the dosage of your choosing to the surface of the pool and run the filter 24/7 until the pool is clear.
Flocculant is great if you want fast results! However, it does require some physical work and you will lose some of your water.
How this works is instead of making the cloudy debris larger to get caught in the filter this simply makes all the particles sink to the floor. From there, you vacuum the pool to waste and remove all the debris. You should have clear water from there.
If you have a cartridge filter I would go ahead and remove the cartridge before you apply the floc. If you have a sand or DE filter then move the valve to "recirculate". This will essentially bypass the filter so the floc doesn't go into the filter. Once that is done go ahead and apply the floc evenly across the surface and allow the system to run for 2 hours. Once that is done turn off the system and make sure it won't turn back on (even turn off the breakers for good measure). Then you want the water to sit still for 24-48 hours to allow everything to sink. Usually you can treat in the evening and the next morning get started with vacuuming. Vacuum slowly. We don't want to cloudy stuff on the bottom to be disturbed. TIP: Check the weather. If it's set to rain during the treatment postpone it. The rain hitting the water would be enough to disturb the process.
If you have any questions or want help please don't hesitate to reach out. Let us help you choose what's best!