Ich bin Pierre. Ich bin1 12 Jahre alt und wohne in Toulouse. Ich habe einen älteren Bruder. Er heisst Cédric. Er ist 16 Jahre alt und er nervt mich oft. Ich lerne Deutsch im ersten Jahr. An Deutschland finde ich2 die Geschichte interessant. Sie ist wichtig für Europa und ich möchte gerne nach Berlin reisen3.
Since I only know spoken French (your spelling drives me nuts) I'm going to write my explanations in English. Feel free to ask about anything you don't understand.
1 - Age is an "inner" property of a person. You have to use a form of the verb "sein" (ich bin, du bist, er ist ...) to describe that kind of property. The verb "haben" is used for "external" properties like eye or hair color for example.
"12 Jahre alt" is the complete form needed. However, in everyday speech people only say "12" (without adding "Jahre alt") so: "Ich bin 12" or "Er is 16" is less formal but still correct. You should use one or the other and not say "Ich bin 12 Jahre" without adding "alt" because this is seen as incorrect by at least some speakers.
2 - German is called a V2-Language. That means the verb in a main clause is always at the second (grammatical) position.
3 - Ok, this is where German is a bit odd. We don't have a word like "go" that can be used generally like "I like to go to Berlin". Instead in German you indicate how the movement takes places. If you say "nach Berlin gehen" the meaning is that you want to walk to Berlin. If you say "nach Berlin fahren" you indicate that you will use some means of transport. I choose the verb "reisen" since it does not indicate the means of transportation but instead says that you want to travel there for a visit.
Secondly, Since I've said before that the verb must go to the second position in the sentence why did I put "reisen" last? That is because the verb in this sentence is "möchte". "Reisen" is part of the predicate though but it is an infinitive and as such not a verb.
1.) Perfekt
Paul _ist_ mit seiner Freundin Laura ins Kino gegangen. Sie haben sich um vier Uhr getroffen. Vorher sie haben sich über Filme unterhalten._Vom Treffpunkt zum Kino sind es nur 15 Minuten zu Fuß gewesen._
2.) Präteritum
Paul ging mit seiner Freundin Laura ins Kino. Sie trafen sich um vier Uhr. Vorher _unterhielten_ sie sich über Filme. Vom Treffpunkt zum Kino _waren_ es nur 15 Minuten zu Fuß.
That is german. Irregular and complicated.----->----->----->----->----->---->----->------->----^
An addition to thtomate's correction:
Vorher haben sie sich über Filme unterhalten.
Remeber the V2-Rule. The word "vorher" is an adverbial but "sie" is the subject of the sentence. "Vorher sie haben.." would be Adverbial + Subject + Verb. The verb comes only third which is impossible in German therefore verb and subject have to change places.
Vielen dank.
Now I want to say, that I've chosen german because I want to know a lot of german people and their history, because germany is very important for the history of my country.
Ich habe deutsch gewählt, weil ich viel1 über die Deutschen und ihre Geschichte wissen möchte1, denn2 Deutschland ist sehr wichtig für die Geschichte meines Landes3.
1 - I've told you about the V2-Rule but, alas, it only applies to independent clauses. Subordinate clauses are an entirely different kettle of fish. The full classification of German's word order is V2-SOV which means that in independent clauses the V2-Rule applies, making the verg go in second position, but in dependent clauses SOV order is applied meaning Subject-Object-Verb. The conjunction "weil" introduces a dependent clause. Thus the verb must be in the final position.
2 - The conjunction "denn" can be used to mean the same as "weil". However while "weil" is a so-called subordinating conjunction that is followed by a dependent clause, "denn" is a coordinating conjunction followed by an independent clause. The conjunction, by the way, is not really part of the clause. Otherwise I'd have to move "ist" one position to the front (V2-Rule for independent clauses).
It is generally better to avoid deep chains of dependent clauses. Therefore "weil ... weil ..." while technically correct is considered bad style. The conjunction "denn" provides an elegant escape from that situation.
3 - Posession is expressed by the genitive case. Although in informal speech "von + dative" is often used, this is considered bad style.
