洗澡(xǐ zǎo) - to have a bath, to have a shower, to wash oneself in Mandarin

洗澡 means washing your whole body and covers both a bath and a shower; Chinese does not force the distinction. If you must be specific, 洗淋浴 or 冲澡 is a shower and 泡澡 is a soak in the tub.

It is a separable verb, so anything that would normally follow the verb goes between the two characters instead. 洗个澡 for have a quick wash, 洗了澡 for washed, 洗完澡 for finished washing, 洗过澡 for have washed before. Saying 洗澡了个 or 我洗澡他 is not possible, which also means 洗澡 can never take an object of its own.

Note the tone sandhi: two third tones in a row, so the first is pronounced as a rising second tone, xí zǎo. The written pinyin keeps both third tones because the underlying tones have not changed.