Learn Russian: Почему ты редко помогаешь бедным семьям?

The verb помогать (to help) always requires the person or thing receiving the help to be in the dative case. Think of it as giving your help to someone. Therefore, poor families becomes бедным семьям.

How did the noun семья become семьям?

Семьям is the dative plural form of семья (family). Nouns that end in the soft vowel -я take the soft dative plural ending -ям.

Why does the adjective бедным end in -ым instead of -им?

Бедным matches the dative plural noun семьям. Because the dictionary form бедный (poor) has a hard stem (the consonant right before the ending is hard), it takes the hard dative plural ending -ым. If it were a soft-stem adjective, it would take -им.

Why is there a soft sign (ь) at the end of the verb помогаешь?

This is just a spelling rule to remember for the ты (you, informal) form of verbs. In the present tense, the ты conjugation always ends in -шь, complete with the soft sign.