CSE contains some important subject like

• Data structures
• Algorithm
• Programming language (c/Java/c++/php/js/.net/swift/ajax/ python)
• Compiler design
• Mathematics
• Electronic communication
• Principal of programing language
• Computer network
• District mathamatic
• Theory of computer
• Computer architecture
• Computer graphics and multimedia
• Fundamental of computer science
• Digital electronic
• Database management system
• Algorithm design
• And so one

Hello,
I am assuming that you want to take admission in cse and before it you want knowledge of it.

You can try to learn basic languages and try to get knowledge about computer system and their working.Try to start programming with C.Get basic concepts from it and start basic programming until you join a college.
Try to gain some information about operating system and data structure(linked list,stack,queue,tree,etc) as these are gonna be very important for you.
Good luck.