la mano NOUN hand
Most Spanish nouns ending in the letter ‘-o’ are masculine, because they are derived from masculine Latin nouns ending in ‘-us’; for example amigo, a (male) friend, from the Latin amicus.
Unfortunately, as with many rules, there are exceptions. The word mano (from Latin manus) is one of the few Spanish nouns which end with the letter ‘-o’ but which are feminine.
Can you give me a hand? ¿Me echas una mano?
Have you washed your hands? ¿Te has lavado las manos?
Make sure you use the correct definite or indefinite article, la/las or una/unas.
The Spanish word moto (motorbike) is also feminine, because it’s short for motoclicleta, as is foto (photo), short for fotografía.
I took a photo of the children. Les saqué una foto a los niños.