How do you know what vowel sounds to use without niqqud? I was surprised that in אתח, the alef is pronounced like an a, but like an o in לא. I've been having trouble figuring out vowel sounds in general, even if I can get the basic feel of how the word is pronounced from the consonants, the vowels throw me off.
It is indeed a challenging matter, and the reason why Hebrew is taught in Israeli grade school with Nikkud for at least half of the first year if not more. Context is key - after you learn the basic patterns you should definitely be able to read without it, but it's definitely way harder to learn without nikkud off the bat.
I see you've reached level 10 in Spanish. Let me use an example from Spanish. If a Spanish sentence is "El hombre come pan.", do you translate it "The masc. man eats bread"? Of course not. You don't here either. You just choose a masculine singular pronoun to go with a masculine singular verb or a feminine singular pronoun to go with a feminine singular verb.
There are two words that could be used. אב (av) is more formal and is like "father" in English. האב (ha-av) would be "the father". אבא (aba) is the less formal word that is more like "dad" in English. This course teaches האבא (ha-aba) as "the dad", but some argue that that is not grammatically correct and that it is always אבא and never האבא.