Good question!
First off, our Keyword Explorer and Tag Suggestions tools provide a ton of great information collected in various ways but both require a human (you) to decide what makes sense and what to use. Use common sense and pick tags that are relevant to your video - don't blindly take our suggestions.
Search Volume
First and foremost, YouTube does not provide public search volume statistics on YouTube. We can get an estimate based on how many search results there are, how many views the search results have and how many search results there are on exact matches of your search term. In addition, we tie in with a trusted 3rd party provider of YouTube search data (https://keywordtool.io/). Using a formula containing these values, we come up with an estimated search volume.
Competition
Competition is another relative score based on several factors. We look at how many results there are, how many views the videos results have. How many times your search term appears in the Title, Tags and Description of each video in the results. How big the channels are in the search results. All of these things help predict how hard it would be for you to rank high in the search results.
Optimization
This section corresponds to how well optimized the search results are. Do the top ranking videos use the keyword in their Titles? In their descriptions & tags? Are there exact matches or just partial matches? All of this factors into a score.
Score
Score is based on Search Volume, Competition and Optimization. Ideally, you want something searched often without much competition and without many results that are optimized well for it.
Whether or not you rank in search results for a particular search phrase is an extremely complex algorithm based on many factors that we don't have access to such as channel authority, session watch time, etc. Generally speaking, we feel like it's most important to focus on more specific searches unless you have a huge channel with very high authority on YouTube.
You can use your "Weighted Score" to get a good sense of whether or not you have a good chance at ranking for a particular keyword.