mir means "to me". This is a dative case of the personal pronoun "ich".
gehen Sie is imperative. This is a way to give commands. If you are talking with someone in a polite manner, you just use the infinitive of the verb, and add "Sie". Don't forget the "Sie".
abbiegen means "to bend". It is a verb with a separable prefix. The root of the verb is in the standard second place in a sentence, and the prefix goes to the end of the sentence.
Postamt is the old-fashioned way to say Post.
The preposition zu is used when going to different services (shop, bank, post office...). When you travel to cities or countries, you will use "nach".
Ampel is a feminine noun. Here we are talking about the location where a person should cross the street. When we talk about a location, we use the dative case. So the definite article becomes "der".
The literal translation would be "The supermarket finds itself behind the big building there". Some verbs use reflexive pronouns ("sich" in this case) and are called reflexive verbs.
Again, we are talking about a location, so the dative case is used.
geöffnet is actually the past participle of the verb "öffnen". But this sentence is not in the past. Past participles of verbs can often be used as adjectives, so "geöffnet" here is used as the adjective "opened". We will talk about the past tense in the German language in lessons to come.
Here we see the dative case again. Note that the adjective "zweite" (second) is also in dative. We will talk about adjective declension soon.
aussteigen (to get off, to step off) is a verb with a separable prefix.
Key phrases
Entschuldigung, können Sie mir bitte sagen, wo die Post ist?
Gehen Sie hundert Meter geradeaus.
Die Bank ist in der Nähe.
Der Supermarkt befindet sich dort hinter dem großen Gebäude.
Steigen Sie an der zweiten Station aus.
Questions
1. Ich kann _ _ _ ? Marktplatz nicht finden. 2. Überqueren Sie dort _ _ ? _ _ _ ? Ampel die Straße. 3. Hier gibt es _ _ _ _ _ _ ? Marktplatz. 4. Steigen Sie an der zweiten Station _ _ _ ?. 5. _ _ _ _ ? es in der Nähe einen Supermarkt?