WHICH TIME I SHOULD USE LES OR DES

salut a tous ANY BODY CAN HELP ME WHICH TIME I SHOULD USE "DES" OR" LES" I KNOW ABOUT WHEN le la =les and un une= des but i dont understand which time should use it for EX merci pour les fleurs why i cant say merci pour des fleurs this is my problem les or des

Salut Sir Alex, If you are ever unsure about which one to use, just translate it back to English to see which one sounds more correct. Taking your examples of; "merci pour les fleurs" et "merci pour des fleurs". Let's just translate them into English, "thank you for the flowers" and "thank you for some flowers". Can you see how the second one just doesn't sound right? Les = the and Des = some I hope this helps - J'espère que cela vous aide. - Marie-Claire