This is the 7907th most frequent Polish word.
mokry
Wet
Here, 'mokry' is used as an adjective describing the state of the sidewalk which has been made wet by the rain.
Dzisiaj pada deszcz, dlatego chodnik jest mokry.
It is raining today, so the sidewalk is wet.
In this sentence, 'mokre' is the plural form to agree with 'ubrania' (clothes), describing their wet condition.
Po godzinie spędzonej na podwórku, moje ubrania są całe mokre.
After an hour spent outside, my clothes are completely wet.
The word 'mokrych' here is in locative case form, agreeing with 'butach' (shoes, plural), to specify the condition of the shoes.