Questions about how keywords work.

[Mansplain]

I am uncertain how keywords are interpreted by the search engine. Can someone help me understand? For example, let's say I've researched through Vid IQ or tubebuddy that "red car" is a keyword that I want to use. Do I have to use red car by itself to be seen as "red car" by the search engine, or will it still be seen as "red car" when I use it in a sentence for example: "costs of insuring a red car". I'm just unsure of when the whole phrase is considered a long-tail keyword. Another example would be: if I had researched and decided that "cost of insuring a red car" and also "red car" were keywords that I wanted to use, would the phrase "cost of insuring a red car" cover both keywords "cost of insuring a red car" and also "red car"? I know it may be a dumb and confusing question, but there are a lot of short keywords that I'd like to use and I don't want to put them in sentences if that affects how they are interpreted by the search engine. Thanks in advance.