Words such as 'weil' and 'obwohl' are known as 'subordinating conjunctions' - these types of conjunctions affect the word order in German. They introduce a clause which cannot stand on its own, but is dependent on the main clause. For example, in English, 'I play football because it's fun.', the main clause is 'I play football', while the subordinate clause is 'because it's fun.'. In German, when 'weil' appears, the conjugated verb must be sent to the end of the clause. For example, the translation of the above sentence would be 'Ich spiele Fußball, weil es Spaß macht.', rather than '*ich spiele Fußball, weil es macht Spaß'. It's also important to make sure you write a comma before the subordinating conjunction as this clearly indicates the clause structure of the sentence. The same rule applies for other subordinate conjunctions such as 'obwohl' which means 'although': 'Ich spiele Fußball, obwohl es anstrengend ist.' In the above examples, the main clause comes first and the subordinate clause comes second. It should be noted that it's perfectly acceptable in German for this order to be reversed - the subordinate clause can come before the main clause: 'Weil es Spaß macht, spiele ich Fußball' and 'Obwohl es anstrengend ist, spiele ich Fußball.' As seen in the above example, when the subordinate clause comes before the main clause, the conjugated verb of the following main clause must be inverted, that is to say come before the subject. A handy way of remembering this, is that it forms what I like to call a 'verb-comma-verb sandwich'.