SPOILER-FREE Guide:
First step: OPEN THE DATABASE CHECKER!!! It will help you to know how much have you unlocked. Take into consideration that you have to refresh it manually.
Second step: start searching with the first word written in the search input ("murder"), watch the videos returned by the query and from these videos get possible keywords, these can be anything (names, objects, places, concepts, etc.). Your queries are by default limited to five results, take that in consideration. Your queries can have multiple words (e.g.: two persons names). In case you're looking for a specific sentence you can type the desired sentence using inverted commas. Think of this as a Google search (but you can't use "+" or "-" afaik). One cool tip: Search "" (empty) and it will return the first five videos!
If there is any doubts on how to do these searches you can check the readme file that appears in the game desktop ;)
Once you watched a certain amount of "important" videos there will a chat notification, open it. There someone will ask you a couple of things, answer with "yes" and it will lead to the game end:
Third step: Use "ADMIN_UNLOCK" (as a query) to increase the search limit from 5 to 15 results and keep searching. Once you had exhausted all possible ideas for keywords you should start using the command "ADMIN_RANDOM", this way you will unlock the remaining videos. Just one note on these admin commands: they're only available once you finish the game.