'Struggle' means strenuous effort; "the struggle to get through the crowd exhausted her" 'Struggle' could also mean: an energetic attempt to achieve something; "getting through the crowd was a real struggle". 'Fight for' usually suggests a cause "I had to fight for my place inn this school" These phrases can be used in a similar way though. They could mean: make a strenuous or labored effort; "She struggled for years to survive without welfare"; "He fought for breath" I hope this helps :)

'Struggle' suggests more difficulty. Here are some visual images: The word 'fight' brings up an image of someone with a sword, for example, striking their opponent. The word 'struggle' suggests someone being held by their opponent, perhaps with their hands behind their back, making desperate movements to break free. I hope those images help you understand the difference.