This is the 13528th most frequent Russian word.
настольному
"Relating to table" or "board (game)."
In this sentence, "настольному" is used as an adjective describing "теннису" (tennis), indicating the type of tennis as 'table tennis'.
Настольному теннису мы уделяем много времени.
We devote a lot of time to table tennis.
Here, "настольному" is an adjective in the dative case describing "компьютеру" (computer), specifying it as a desktop computer.
Я предпочитаю настольному компьютеру мобильный.
I prefer a mobile phone to a desktop computer.
In this sentence, "настольному" modifies "футболу" (football) to express the type of football, which is 'table football'.