I`m at 10th and I know that I need to prepare for jee mains right from 11th but I`m getting confused that the topics for jee mains and ncert different if it is by how how many chapters And which is the best book for maths

dear ayan 
only 2-3 topics are diffrent , not much , jee mains is a majority ncert based test , 
so, nothing to worry about . 
just do the topics that are there in ncert but with proper understanding . jee will test your application based knowledge . 
for maths , go with iit maths by m l khanna , thats the best book for all catagory like algebra , trigo , calculus etc .. 
HOPE IT CLEARS 
REGARDS