Conjunctions connect sentences and phrases, therefore we will have a short look at the ost important ones.
He goes swimming although he is ill.
He goes swimming because it is fun.
Conjunctions establish a logical connection between phrases. They can be quite different as we can see in the phrases above. Some conjunctions do also have a certain function of opening a sentence in certain tenses, to which we will come back a bit later. We will now start with the most common and simple ones.