The 3 times table lists the multiples of 3: 3 × 1 = 3, 3 × 2 = 6, … 3 × 12 = 36. "3x" usually refers to this multiplication table.
"3x" can mean 3 times a variable, but most people searching it want the 3 times table: 3 × 1 = 3, 3 × 2 = 6, … 3 × 12 = 36.
Learn the multiples of 3 from 3 × 1 = 3 up to 3 × 12 = 36. Count up by 3 each time, or drill yourself with the table above.