The three variables define the type of matches and the score each match receives. An increased value/score will make the kind of match more relevant. If you don't want partial words to match then set $t_partial_match_score to zero for example.
You are welcome to experiment with the values to see what works best for you.
Below is a fairly accurate explanation of how results are ranked or the formula being used.
Each keyword matched in a listing gets a score, according to the matches found. A match in the 'title' will provide a certain score. The description & keyword fields also has a certain score. AND and OR matching also plays a factor and AND matches are given a high score where OR matches does'nt really provide a good score. Phrase matches for example 'music videos' also receives a good score. Everything is added up for each link and sorted from most to least score. The links with the best scores are listed first and the links with the least are listed last.