Well, the most correct translation for "What do you mean?" would be "Что ты име́ешь в виду́?" (mean = име́ть в виду́). But both phrases can be used in the same situation, so they are synonymic.

I thought the same

no

Yes, these words are related. Сказать → сказка (because сказка, fairy tale, is a story that you are saying/telling)

Что is 'what' and как is 'how'. For example: Что это слово? - What is this word? Как сказать это слово? - How do you say this word?

I think this is correct. Somebody verify this!

no

It has 6 forms for the non-past. It is pretty common for European languages (except English). The verb has an irregular conjugation: its singular and plural forms follow different schemes (хочу́, хо́чешь, хо́чет / хоти́м, хоти́те, хотя́т).

• a regular verb of И-conjugation: говорю, говоришь, говорит, говорите, говорят.
• a regular verb of Е-conjugation: знаю, знаешь, знает, знаем, знаете, знают.

The 4 past forms are nothing to write home about, though. The infinitive is хотеть. Remove the -ть and add -л, -ла, -ло depending on the gender of the subject—use -ли for plural subject. Pretty much every Russian verb works like that, with exceptions few and far between.

all verbs have 6 forms for present and future tense. each form corresponds with a personal pronoun. that is I want, you want, she he it wants, and same fr plural. this means that you can skip the pronoun and just say "want chicken", and from the form want takes, you will know if it's me who wants the chicken, or them, or us, or whatever.

I think "tell" would be "raskazat"

In life it would be appropriate. In Duolingo it won't, because "What are you trying to say?" literally = "Что ты пыта́ешься сказа́ть?"