Is there a point system or weight value assigned to Questions, Tags and answers when searching by a keyword?
Tags, Questions then answer...or a score?
Evaluates different aspects, such as title words (for Q only), content words (for Q, A, C), tag words (for Q only) and the handle of the users. Also the hotness too. All the matches are weighted differently, even for same words matching different questions will generate different scoring because the id of the questions is used while weighting. Besides, if the word is too common, then it won't be considered.
Regarding the specific weight applied to content words it is Q = 1, A = 0.5 and C = 0.25 (I think NOTEs are matched to at 0.25) but the relationship to get the scoring is not simply linear as you suggested as the formulae are slightly more complex.
If that's true, how does it order them?
Once all scores of the different aspects (titles, content, tags, handles) are calculated they are summed up and joined to the relevant questions (lists only display questions, not answers or comments but can link to them). In this step also hotness is taken into consideration and, again, the question ID (the higher, which means the more recent, the better). Sorting is descendant by score.
I don't see relevance, should it be order be Questions: 1, 3, 2, 5 and 4 at best?
It is impossible to know because you should evaluate all aspects and you are missing handles, post ids, hotness and have even merged the title and content aspects.
Is there a way I can add more "points" or weight to each, question, tag and answer?
Yes. Check here (code linked to v1.7.4): https://github.com/q2a/question2answer/blob/4fce0eb2390f56b645dad375d1d81e9f91a97e69/qa-include/db/selects.php#L712
Look for all the mentions to "score" (usually near to a logarithm). Just update the query in that point.