This is the 17188th most frequent Russian word.
столу
"Столу" means "to the table" in English.
Analyzing the sentence, 'столу' is the dative form of 'стол' which is a noun meaning 'table'. It is used here to indicate the direction of movement toward the table.
Я подошёл к столу.
I approached the table.
In this sentence, 'столу' is the dative case, used to convey the idea of placing an object in proximity to the table.
Книгу я положил к столу.
I placed the book near the table.
Although not featuring 'столу', the case use of 'столом' here is instrumental, showing a different case usage of the root word 'стол' in context. This is to display case relationships for teaching.