6. What’s the difference between “если” and “ли”? Do they both mean “if”?

It's very easy to mix up the words "ли" and "если" when you learn Russian because both words can be translated into English as "if". In Russian they are quite different from each other. Let's see how to use them correctly.
We use "если" to express a condition:

• Если завтра будет дождь, я буду дома. = If it rains tomorrow I'll stay at home. Pay attention that in Russian, we have to use future in both parts of the sentence (будет дождь, я буду дома).
• Ты можешь взять мой велосипед, если хочешь. = You can take my bike if you want.
• Если я буду в городе, я позвоню тебе. = If I'm in town I'll call you.

We use "ли" to express a doubt about something. You can also translate it as "whether". In fact, try to associate "ли" with "whether" in your mind and you won't mix it up with "если" any more. Let's have a look at the examples:

• Я не знаю, будет ли завтра дождь. = I don't know whether tomorrow it's going to rain.
• Я спросил его, хочет ли он взять мой велосипед. = I asked him whether he wanted to take my bike.
• Я не знаю, буду ли я в городе. = I don't know whether I'm going to be in town.

Where should I put "ли" in a sentence? We usually put "ли" after the word that expresses the actual doubt. Compare these sentences:

• Я не знаю, купил ли он хлеб. = I don't know whether he bought bread.
• Я не знаю, хлеб ли он купил. = I don't know whether it was bread that he bought (or something else).
• Я не знаю, он ли купил хлеб. = I don't know whether it was him who bought the bread.

As you must have noticed the "doubt" always comes first in the subordinate clause. If you change the word order you will also change the focus of the doubt.

9. How should I use "нравиться" in Russian?

When you translate “I like” into Russian you might have some difficulties, as the verb “нравиться” is not exactly “to like”, but rather “to be liked”, or “to be enjoyable, pleasing”. Compare:

• Мне нравится книга. = I like the book (literally we say: "the book is liked by me/the book is enjoyable for me").

Pay attention that "the book" or "what you like" is in the nominative case because it's the subject of the sentence and the verb “нравиться” agrees with it (depends on its gender and number (singlular or plural)). Accordingly, "the one who likes" would be in the dative case:

• Книга нравится. Кому? Мне. = The book is enjoyed. By whom? (who enjoys it?) (By) me.

When "what you like" is expressed by an infinitive, "нравиться" will be in the 3d person, neuter. For example,

• Мне нравится читать. = I like reading .
• Мне нравилось читать раньше. = I liked reading before.

Note that the verb "нравиться" has all the conjugation forms": "я нравлюсь, ты нравишься, он нравится, вы нравитесь, мы нравимся, они нравятся". But be careful! The grammar structure is the contrary to the English one, and it looks very misleading. Compare:

• Я нравлюсь ему. = He likes me (literally, "I am liked by him").
• Ты нравишься нам. = We like you. (literally, "You are liked by us").

Attention! The perfective form of "нравиться" is "понравиться" . It means that you will mostly use it for a single occasion and/or with a certain result in the future or the past. Important that we use this form to express our opinion (= in English: I love it! I loved it!). For example:

• Мне понравилось шоу. = I liked (loved) the show.
• Я уверен, шоу мне понравится . = I am sure, I will like (love) the show.