Learn Portuguese (Portugal): Assa as maçãs no forno.

Assa is the informal command for tu (you). When giving a command to a friend, you use the same form as the normal he/she/it present tense. If you were speaking formally to someone using você, you would change the ending and say asse.

Does assar mean to roast or to bake?

It can mean both! Assar is used for cooking food in dry heat, usually in an oven (forno). You use it for roasting meat, fish, or vegetables, and also for baking things like apples or potatoes. However, baking cakes or bread usually uses the verb cozer.

Why does the sentence use no forno instead of just em o forno?

In Portuguese, the preposition em (meaning in, on, or at) must always combine with the word o (the) to form no. It is a mandatory contraction, so you will never see em o written as two separate words.

How do the special marks change the pronunciation of the word maçãs?

The mark under the c is called a cedilla and it forces the ç to make a soft s-sound rather than a hard k-sound. The wavy line over the second a is a tilde, which tells you to make a nasal sound through your nose, similar to the vowel sound in the English word sung.