One problem in English is that it's very hard to tell whether a word is a verb, a noun, an adjective, or something else. (In Polish it's easier. Verbs usually tend to end in ć, for example.)
The example to look at today is the word afraid. In English, this is an adjective (przymiotnik), not a verb. Many Polish students are confused by this, because in Polish we use a verb, not an adjective, to express this idea:
Boję się niedźwiedzia.
But we cannot say in English "I afraid of the bear." Afraid is not a verb, so it makes no sense to say "I afraid, you afraid, he afraids, etc." Instead, we say: "I'm afraid of the bear," in the same way we would say "I'm hungry, I'm happy, I'm old." Here are a few sample sentences:
He's afraid of ghosts.
They're afraid of the dark.
Who's afraid of the big bad wolf?
As long as we're talking about "afraid," here's something else to think about.
We use afraid of + a noun or a noun phrase, as in the examples above: afraid of ghosts, afraid of bears, etc. But we say afraid that + a verb phrase. What's a verb phrase? Well ... it's a phrase including a verb or verbs, very similar to a sentence. Here are some examples, with the verb phrase in bold type and the verb or verbs in italics:
He's afraid that the ghosts will eat him for dinner.
They're afraid that they might get lost in the dark.
Who's afraid that the big bad wolf is going to attack him?
In English we do have a verb that works like bać się in Polish. That verb is to fear. It's a bit old-fashioned now and people usually don't use it; they prefer to be afraid.
I fear bears.
I fear that the bears will move into our house.