New player combat confusion

Hi I’m really new to osrs and I’ve been told to do as many quests as possible and really enjoying it. Problem is a lot of these quests have enemies to defeat. I have done waterfall quest so I’m 30 attack and strength but only 11 defense. All the next combat quests seem really difficult with high lvl enemies. Do I need to go train somewhere and if so how. Every guide says to quest but they are all super hard