The preposition за has multiple meanings and is used with several cases. One of those meanings is in sentences where someone goes somewhere to purchase something, where it is used with the instrumental case:

The preposition doesn't necessarily imply purchasing.

It can also be used for picking someone up on the way somewhere:

The word for nothing in Russian is ничто. Grammatically we call it a negative pronoun, and as a pronoun of course it occurs in all six cases:

The first curious thing to note about the word is that you rarely encounter the nominative case form; instead you often find the genitive. For instance, if you wanted to say “nothing helped,” you might expect the translation to be «ничто не помогло». That is a perfectly grammatical sentence, but more often you would hear something like this:

That's not to say you won't ever see ничто. Back around 1997 there was an advertising campaign in Russia for Sprite. It began with posters of sexy models that said «Имидж ничто…» “Image is nothing…” and followed a while later by another set of posters with sexy models that said «Жажда всё» “Thirst is everything.” I remember being confused when I saw the first set of signs because they had nothing about Sprite on them, but weeks later I understood it when the second set of signs appeared that included Sprite images. Apparently the campaign worked: even a decade later you can still find people playing with the phrase. For instance, at the beginning of this month there was an article on podrobnosti.ru entitled «Имидж ничто, ответственоость всё» “Image is nothing; responsibility is everything.” The phrase has even penetrated popular humor:

“Image is nothing; thirst is everything. I won't let myself dry out.”

It's worth remembering that once you put a form of ничто in a sentence, you must also include the negative particle не before the verb. And if ничто is the object of a preposition, the ни separates from the rest of the word and moves in front of the preposition:

In conversation ничего acquires a wide range of meanings:

Thus in the end nothing means a lot of different things. Ironic.

Лучше means better. It can be used either as an adverb or as a short-form adjective.

If you want to include a “than” in the sentence, then the word you want is чем:

Interestingly enough, if the чем is followed by a noun or pronoun in the nominative case, you can make an equivalent construction by dropping the чем and using the genitive of the noun/pronoun:

Лучше is also often used with future tense verbs or imperative verbs to express the idea of “it would be better”:

Last but not least, here we have a standard mother-in-law joke that uses the word:

When a plane or flying animal lands, the landing can be expressed by the verb садиться/сесть. There is a subtlety in the use of the prepositions with this idea. First off, if you land on something, then that is often expressed by motion phrases with the accusative case:

But the location where the craft lands (not the the thing it lands on) is expressed with location phrases:

1963 — Neva River

The verb садиться/сесть is also used to express the idea of boarding a bus, train, plane, or car: