Keep watching videos, they will help if you have absolutely nothing in a Bug-out situation.
No self-made will ever be as effective as a store bought filter...but...using a self-made to PRE-treat the water in question before it is run thru a store bought one will extend the filter life of your store-bought filter.
Having several small filters in your BOB and INCH bags, combined with a larger one to be transported in your bug-out-vehicle and an expensive one in your house till you have to bug out is the right combination.
Also have your chlorine dioxide tabs, mixes or pre-mix with you for last ditch help. Storing your thousand liters/ 250 gallons of water with some micropure tabs, chlorine, potassium manganate, MMS/CDS or such is also advisable. Not so much for the SHTF but for if you lose water for a short period of time from catastrophes and bad water from working accidents in your local towns watersystems.....stored water will hold for over a year with my experiences but you can change it out, clean the container and refill at will and desire. If nothing else, water the garden or flush your toilets and pipes with the now unwanted ex-stored water.