A conjunction is a word which joins two clauses together. For example, in English:

I would love to come to your party but I’m washing my hair that night.

She works hard, although she’s a total maniac.

Or in German:

Wir machen ein Picknick und gehen danach in der Wald spazieren.

Ich spiele jeden Tag Dudelsack, wenn ich Zeit habe.

Click here to read the full lesson on different kinds of conjunctions.