When you learn enough words, it becomes pretty clear which word has which gender.
Basic rules are:
If it is a person who has a gender, the gender of the word is the same. (German learners, you should understand this, "das Mädchen", nothing like this in Ukrainian!) A child ("дитина") and a human/person ("людина") are feminine. Which brings us to number 2...
If it ends with "а" or "я" it is most probably feminine. Right away, I can only think of one word that ends with "а" that is masculine ("собака" - "dog"), and there is also "сирота" (orphan) that can be either masculine or feminine depending on the gender of the person.
If it ends with "о" or "е" or "є" it is most probably neuter. You have already learned the word "дядько", but an uncle is a man, so the noun is masculine.