Learn Spanish (Spain): Una mano tiene cinco dedos.

In Spanish, most words ending in "-o" are masculine, but mano is a famous exception! It is a feminine word, which is why we use the feminine word for "a" here: una mano. You will also always say la mano (the hand).

Why is the verb tiene instead of "tene"?

The verb for "to have" is tener. It is what we call a "stem-changing" verb, which is very common in Spanish. When you conjugate it for he, she, or it (like "a hand"), the "e" in the middle changes to "ie", making it tiene.

Does una mean "a" or "one" here?

It can mean both! In Spanish, the word for the number one (un or una) is the exact same word as the indefinite article ("a" or "an"). Here, it translates perfectly as "A hand", but it could also be understood as "One hand" depending on what you want to emphasize.

Does dedos only mean "fingers"?

Actually, dedos is used for both "fingers" and "toes" in Spanish! Since we are talking about a hand here, it obviously means fingers. If you ever need to be specific about toes, you can say dedos del pie (literally: fingers of the foot).