着 has four readings - pick by context. Toneless
着 is the aspect particle (this entry). The other three are separate words filed on their own pages:
着 ('to touch, to catch, fall asleep, hit the mark'),
着 ('to wear, to apply, to contact'), and
着 ('a move in chess, a trick'). The aspect-particle reading is by far the most common - over 90% of casual usage.