These six conjunctions open a subordinate clause (Nebensatz): it is set off by a comma, and the conjugated verb goes to the very end. The conjunction seems to “take” the verb and send it to the end.
WEILbecauseIch bleibe zu Hause, weil ich krank bin.I am staying home because I am ill.
DASSthatIch weiß, dass er heute kommt.I know that he is coming today.
WENNif; wheneverIch lerne Deutsch, wenn ich Zeit habe.I learn German when I have time.
OBwhether, ifIch weiß nicht, ob er heute kommt.I do not know whether he is coming today.
OBWOHLalthoughIch gehe spazieren, obwohl es regnet.I am going for a walk although it is raining.
WÄHRENDwhileIch höre Musik, während ich lerne.I listen to music while I study.
Watch the verb: after weil it is at the very end
IchlerneDeutsch,weilichZeithabe.
Ich lerne Deutsch, weil ich Zeit habe.I learn German because I have time.dass or dasdass with two s is the conjunction “that”: Ich glaube, dass er kommt. das with one s is an article or a pointing word: das Buch, Das ist gut. Quick test: if you can replace it with dieses or welches, it is das; otherwise it is dass, and the verb of its clause goes to the end.
ob and wennob turns a question without a question word into a subordinate clause: Kommt er? → Ich weiß nicht, ob er kommt. wenn means “if” and “whenever” for repeated or future things. For a single event in the past you need als, which is a separate topic. English uses “if” for both: if you can say “whether”, use ob.
denn or weilBoth mean “because”. denn keeps the verb in second place and cannot start a sentence. weil sends the verb to the end and can open a sentence: Weil ich krank bin, bleibe ich zu Hause. In speech weil is far more common, denn sounds more written.
English “that”English often drops “that”: I think he is ill. German has two correct options: Ich glaube, dass er krank ist. (dass, verb at the end) or Ich glaube, er ist krank. (no dass, normal order). Never mix them.