Subordinating conjunctions are words which send the verb to the end of the clause/phrase (this is sometimes the end of the sentence, but not always). They are common words, and correctly using them shows off your knowledge to the reader. There is no 'rule' to telling if a word is SC, however a few common ones are weil (because), obwohl (although) and obgleich (although). If the SC sends the verb to the end of the clause, and the next clause has a verb, then the correct way to write it is verb , verb e.g. weil ... ist, hat ...